Driver circuit and semiconductor device

ABSTRACT

The silicon nitride layer  910  formed by plasma CVD using a gas containing a hydrogen compound such as silane (SiH 4 ) and ammonia (NH 3 ) is provided on and in direct contact with the oxide semiconductor layer  905  used for the resistor  354 , and the silicon nitride layer  910  is provided over the oxide semiconductor layer  906  used for the thin film transistor  355  with the silicon oxide layer  909  serving as a barrier layer interposed therebetween. Therefore, a higher concentration of hydrogen is introduced into the oxide semiconductor layer  905  than into the oxide semiconductor layer  906 . As a result, the resistance of the oxide semiconductor layer  905  used for the resistor  354  is made lower than that of the oxide semiconductor layer  906  used for the thin film transistor  355.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a driver circuit including an elementthat is formed using a metal oxide exhibiting semiconductorcharacteristics, and to a semiconductor device using the driver circuit.Note that the semiconductor device indicates all the devices that canoperate by using semiconductor characteristics, and display devices,semiconductor circuits, and electronic appliances are all included inthe category of the semiconductor devices.

2. Description of the Related Art

A wide variety of metal oxides exist and are used for variousapplications.

Indium oxide is a well-known material and is used as a transparentelectrode material needed for a liquid crystal display and the like.

Some metal oxides exhibit semiconductor characteristics. Metal oxidesexhibiting semiconductor characteristics are a kind of compoundsemiconductor. The compound semiconductor is a semiconductor obtained bybonding two or more kinds of atoms. In general, metal oxides areinsulators; however, it is known that metal oxides become semiconductorsdepending on the combination of elements included in the metal oxides.

For example, it is known that some metal oxides such as tungsten oxide,tin oxide, indium oxide, and zinc oxide exhibit semiconductorcharacteristics. References disclose a thin film transistor in which atransparent semiconductor layer including such a metal oxide is used asa channel formation region (Patent Documents 1 to 4, and Non-PatentDocument 1).

As metal oxides, multi-component oxides as well as single-componentoxides are known. For example, InGaO₃(ZnO)_(m) (m is a natural number)belonging to homologous series is a known material (Non-Patent Documents2 to 4).

In addition, it has been confirmed that such an In—Ga—Zn-based oxide canbe used for a channel formation region of a thin film transistor (PatentDocument 5, and Non-Patent Documents 5 and 6).

REFERENCES Patent Document

-   [Patent Document 1] Japanese Patent Laid-Open No. S60-198861-   [Patent Document 2] Japanese Patent Laid-Open No. H8-264794-   [Patent Document 3] Japanese Translation of PCT International    Application No. H11-505377-   [Patent Document 4] Japanese Patent Laid-Open No. 2000-150900-   [Patent Document 5] Japanese Patent Laid-Open No. 2004-103957

Non-Patent Document

-   [Non-Patent Document 1] M. W. Prins, K. O. Grosse-Holz, G    Muller, J. F. M. Cillessen, J. B. Giesbers, R. P. Weening, and R. M.    Wolf, “A ferroelectric transparent thin-film transistor” (Appl.    Phys. Lett., 17 June, 1996, Vol. 68, pp. 3650-3652)-   [Non-Patent Document 2] M. Nakamura, N. Kimizuka, and T. Mohri, “The    Phase Relations in the In₂O₃—Ga₂ZnO₄—ZnO System at 1350° C.” (J.    Solid State Chem., 1991, Vol. 93, pp. 298-315)-   [Non-Patent Document 3] N. Kimizuka, M. Isobe, and M. Nakamura,    “Syntheses and Single-Crystal Data of Homologous Compounds, In₂O₃    (ZnO)m (m=3, 4, and 5), InGaO₃ (ZnO)₃, and Ga₂O₃ (ZnO)m (m=7, 8, 9,    and 16) in the In₂O₃—ZnGa₂O₄—ZnO system” (J. Solid State Chem.,    1995, Vol. 116, p. 170-178)-   [Non-Patent Document 4] M. Nakamura, N. Kimizuka, T. Mohri, and M.    Isobe, “Homologous Series, Synthesis and Crystal Structure of InFeO₃    (ZnO)m (m: natural number) and its Isostructural Compound” (KOTAI    BUTSURI (SOLID STATE PHYSICS), 1993, Vol. 28, No. 5, pp. 317-327)-   [Non-Patent Document 5] K. Nomura, H. Ohta, K. Ueda, T. Kamiya, M.    Hirano, and H. Hosono, “Thin-film transistor fabricated in    single-crystalline transparent oxide semiconductor” (SCIENCE, 2003,    Vol. 300, p. 1269-1272)-   [Non-Patent Document 6] K. Nomura, H. Ohta, A. Takagi, T. Kamiya, M.    Hirano, and H. Hosono, “Room-temperature fabrication of transparent    flexible thin-film transistors using amorphous oxide semiconductors”    (NATURE, 2004, Vol. 432, pp. 488-492)

SUMMARY OF THE INVENTION

Application of a thin film transistor using a metal oxide exhibitingsemiconductor characteristics (hereinafter, also referred to as an oxidesemiconductor) to an active matrix display device (such as a liquidcrystal display, an electroluminescence display, or electronic paper)has been taken into consideration. An active matrix display deviceincludes several hundreds of thousands to several millions of pixelsarranged in a matrix and a driver circuit for inputting pulse signals tothe pixels.

In an active matrix display device, a thin film transistor is providedin each pixel and serves as a switching element for switching on or offwhen a pulse signal is input from a driver circuit, so that images canbe displayed. The thin film transistor is also used as an elementforming a driver circuit.

A driver circuit for driving a pixel portion includes elements such as athin film transistor, a capacitor, and a resistor.

An object of one embodiment of the present invention is to provide adriver circuit including an active element and a passive element thatare manufactured using an oxide semiconductor, and a semiconductordevice including the driver circuit.

One embodiment of the present invention includes an enhancement-modethin film transistor and a resistor. The thin film transistor and theresistor are formed using an oxide semiconductor layer. In addition, theconcentration of hydrogen in the oxide semiconductor layer used for thethin film transistor is made lower than that in the oxide semiconductorlayer used for the resistor. Accordingly, the oxide semiconductor layerused for the resistor has a lower resistance than the oxidesemiconductor layer used for the thin film transistor.

One embodiment of the present invention includes a thin film transistorand a resistor that are formed using an oxide semiconductor layer. Asilicon nitride layer formed by plasma CVD using a gas containing ahydrogen compound such as silane (SiH₄) and ammonia (NH₃) is formed onand in direct contact with the oxide semiconductor layer used for theresistor, and the silicon nitride layer is formed over the oxidesemiconductor layer used for the thin film transistor with a siliconoxide layer serving as a barrier layer interposed therebetween.Therefore, a higher concentration of hydrogen is introduced into theoxide semiconductor layer used for the resistor than into the oxidesemiconductor layer used for the thin film transistor. As a result, theoxide semiconductor layer used for the resistor has a lower resistancethan the oxide semiconductor layer used for the thin film transistor.

That is, one embodiment of the present invention is a driver circuitincluding a resistor in which a first oxide semiconductor layer is usedfor a resistor element, a thin film transistor in which a second oxidesemiconductor layer having a lower concentration of hydrogen than thefirst oxide semiconductor layer is used for a channel formation region,a silicon oxide layer provided over the second oxide semiconductorlayer, and a silicon nitride layer provided over the first oxidesemiconductor layer and the silicon oxide layer.

According to one embodiment of the present invention, an oxidesemiconductor layer having a low resistance may be provided between theoxide semiconductor layers that are used for the resistor element of theresistor and the channel formation region of the thin film transistor,and a wiring that is a conductor.

That is, according to one embodiment of the present invention, thedriver circuit having the aforementioned structure includes a thirdoxide semiconductor layer in contact with one terminal or the otherterminal of the resistor and the first oxide semiconductor layer; afourth oxide semiconductor layer in contact with a first terminal of thethin film transistor and the second oxide semiconductor layer; and afifth oxide semiconductor layer in contact with a second terminal of thethin film transistor and the second oxide semiconductor layer. Theresistance of each of the third oxide semiconductor layer to the fifthoxide semiconductor layer is lower than that of the second oxidesemiconductor layer.

In addition, a driver circuit of one embodiment of the present inventionincludes a resistor and a thin film transistor that are formed using anoxide semiconductor layer containing a high concentration of nitrogen.Furthermore, a silicon oxide layer serving as a barrier layer isprovided over the thin film transistor. At this time, heat treatment isperformed at 200° C. to 600° C., typically 250° C. to 500° C. in anatmosphere containing a substance which is a supply source of a hydrogenatom. Nitrogen in the oxide semiconductor layer has the effect ofpreventing atoms forming the oxide semiconductor layer from tightlyfilling the film, and of promoting diffusion and solid dissolution ofhydrogen in the film. Accordingly, the heat treatment allows a higherconcentration of hydrogen to be introduced into the oxide semiconductorlayer used for the resistor and containing a high concentration ofnitrogen than into the oxide semiconductor layer used for the thin filmtransistor. As a result, the resistance of the oxide semiconductor layerused for the resistor and containing a high concentration of nitrogen islower than that of the oxide semiconductor layer used for the thin filmtransistor and containing a high concentration of nitrogen.

That is, the driver circuit of one embodiment of the present inventionincludes a resistor in which a first oxide semiconductor layercontaining a high concentration of nitrogen is used for a resistorelement, and a thin film transistor in which a second oxidesemiconductor layer containing a high concentration of nitrogen and alower concentration of hydrogen than the first oxide semiconductor layeris used for a channel formation region.

Note that the oxide semiconductor layer containing a high concentrationof nitrogen refers to an oxide semiconductor layer with a ratio ofnitrogen (N) to oxygen (O) (N/O) of 0.05 to 0.8, preferably 0.1 to 0.5.

Furthermore, according to one embodiment of the present invention, asilicon nitride layer formed by plasma CVD using a gas containing ahydrogen compound such as silane (SiH₄) and ammonia (NH₃) is provided onand in direct contact with the oxide semiconductor layer used for theresistor and containing a high concentration of nitrogen.

That is, according to one embodiment of the present invention, thedriver circuit having the aforementioned structure includes a siliconoxide layer provided over the second oxide semiconductor layer, and asilicon nitride layer provided over the first oxide semiconductor layerand the silicon oxide layer.

In this document (specification, claims, drawings, and the like), theword “film” means something formed on the entire surface of a substrateto be processed into a desired shape in a subsequent photolithographystep or the like, and something before the processing. The word “layer”means something obtained by processing and shaping a “film” into adesired shape by a photolithography step or the like, or something thatis to be formed on the entire surface of a substrate.

Also in this document (specification, claims, drawings, and the like),the phrase “A and B are connected” means that A and B are electricallyconnected, as well as that A and B are directly connected. Here, thephrase “A and B are electrically connected” shows that, when anelectrically acting object exists between A and B, A and B are atsubstantially the same potential through the object.

Specifically, the phrase “A and B are connected” means the case where Aand B can be regarded to be at the same node in consideration of thecircuit operation, such as the case where A and B are connected througha switching element such as a transistor and have substantially the samepotential through the conduction of the switching element, and the casewhere A and B are connected through a resistor and a potentialdifference between the two ends of the resistor does not affect theoperation of a circuit including A and B.

Note that it is difficult to determine which one of the terminals of athin film transistor is a source terminal or a drain terminal because itchanges depending on the structure, operating conditions, and the likeof the thin film transistor. Therefore, in this document (specification,claims, drawings, and the like), one of a source terminal and a drainterminal is referred to as a first terminal and the other thereof isreferred to as a second terminal for distinction.

According to one embodiment of the present invention, the concentrationof hydrogen in an oxide semiconductor layer used for a resistor elementof a resistor can be made higher than that in an oxide semiconductorlayer used for a channel formation region of a thin film transistor.Therefore, the resistance of an oxide semiconductor layer can beselectively lowered. Accordingly, a thin film transistor and a resistordo not need to be manufactured in different steps, which makes itpossible to provide a driver circuit manufactured in a smaller number ofsteps and a semiconductor device including the driver circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a diagram illustrating an example of a structure of asemiconductor device;

FIG. 2 is a block diagram illustrating an example of a structure of adriver circuit;

FIGS. 3A and 3B are circuit diagrams illustrating an example of astructure of a driver circuit;

FIG. 4 is an example of a timing chart of a driver circuit;

FIGS. 5A to 5C are circuit diagrams illustrating an example of astructure of a driver circuit;

FIGS. 6A to 6C are circuit diagrams illustrating an example of astructure of a driver circuit;

FIG. 7 is a block diagram illustrating an example of a structure of adriver circuit;

FIG. 8 is a layout illustrating an example of a structure of a drivercircuit;

FIG. 9 is a layout illustrating an example of a structure of a drivercircuit;

FIG. 10 is a layout illustrating an example of a structure of a drivercircuit;

FIGS. 11A to 11C are diagrams illustrating an example of a structure ofa driver circuit;

FIGS. 12A and 12B are diagrams illustrating an example of a structure ofa driver circuit;

FIGS. 13A and 13B are diagrams illustrating an example of a structure ofa driver circuit;

FIGS. 14A and 14B are diagrams illustrating an example of a structure ofa driver circuit;

FIGS. 15A to 15C are diagrams illustrating an example of a manufacturingprocess of a driver circuit;

FIGS. 16A to 16C are diagrams illustrating an example of a manufacturingprocess of a driver circuit;

FIG. 17 is a diagram illustrating an example of a structure of a drivercircuit;

FIGS. 18A to 18C are diagrams illustrating an example of a manufacturingprocess of a driver circuit;

FIGS. 19A and 19B are diagrams illustrating an example of amanufacturing process of a driver circuit;

FIGS. 20A and 20B are circuit diagrams illustrating an example of astructure of a driver circuit, and 20C is an example a timing chart ofthe driver circuit;

FIG. 21 is a diagram illustrating an example of a structure of asemiconductor device;

FIGS. 22A and 22B are circuit diagrams illustrating an example of astructure of a protective circuit;

FIG. 23 is a circuit diagram illustrating an example of a structure of apixel of a semiconductor device;

FIGS. 24A to 24C are diagrams each illustrating an example of astructure of a semiconductor device;

FIGS. 25A and 25B are diagrams illustrating an example of a structure ofa semiconductor device;

FIG. 26 is a diagram illustrating an example of a structure of asemiconductor device;

FIGS. 27A to 27C are views each illustrating an example of asemiconductor device; and

FIGS. 28A and 28B are views each illustrating an example of asemiconductor device.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the disclosed invention will be described below withreference to drawings. Note that the disclosed invention is not limitedto the following embodiments, and it is apparent to those skilled in theart that modes and details can be modified in a wide variety of wayswithout departing from the spirit and scope of the disclosed invention.Accordingly, the disclosed invention should not be construed as beinglimited to the description of the embodiments given below. Note that inthe embodiments shown below, like portions are denoted by like referencenumerals in different drawings in some cases.

Embodiment 1

In this embodiment, an example of a display device including a drivercircuit manufactured using an oxide semiconductor will be described withreference to FIGS. 1 and 2, FIGS. 3A and 3B, FIG. 4, FIGS. 5A to 5C,FIGS. 6A to 6C, FIGS. 7 to 10, FIGS. 11A to 11C, FIGS. 12A and 12B,FIGS. 13A and 13B, FIGS. 14A and 14B, FIGS. 15A to 15C, and FIGS. 16A to16C. Specifically, a driver circuit having an inverter formed by acombination of an enhancement-mode thin film transistor and a resistor(hereinafter, referred to as an ERMOS circuit) will be described as anexample of a source line driver circuit and a gate line driver circuitthat are driver circuits for driving a pixel portion of a displaydevice. Note that in this embodiment, an n-channel thin film transistoris used as a thin film transistor forming a unipolar driver circuit.

Note that a display device refers to a device including a displayelement such as a light-emitting element or a liquid crystal element.The display device may include a peripheral driver circuit for driving aplurality of pixels. The peripheral driver circuit for driving aplurality of pixels is formed over the same substrate as the pluralityof pixels. The display device may include a flexible printed circuit(FPC). Furthermore, the display device may include a printed wiringboard (PWB) which is connected to the display device through a flexibleprinted circuit (FPC) or the like and to which an IC chip, a resistor, acapacitor, an inductor, a transistor, and the like are attached. Thedisplay device may further include an optical sheet such as a polarizingplate or a retardation plate, a lighting device, a housing, an audioinput/output device, an optical sensor, and the like.

FIG. 1 illustrates an overall view of a display device. A source linedriver circuit 101, a first gate line driver circuit 102A, a second gateline driver circuit 102B, and a pixel portion 103 are formed over asubstrate 100. In the pixel portion 103, a part surrounded by a dottedframe 110 is one pixel. FIG. 1 illustrates an example where the firstgate line driver circuit 102A and the second gate line driver circuit102B are used as a gate line driver circuit; however, only one of themmay be used as a gate line driver circuit. In the pixel of the displaydevice, a display element is controlled by a thin film transistor.Signals (clock signals, start pulses, and the like) for driving thesource line driver circuit 101, the first gate line driver circuit 102A,and the second gate line driver circuit 102B are input from the outsidevia flexible printed circuits (FPCs) 104A and 104B.

The source line driver circuit and the gate line driver circuit fordriving the pixel portion have a logic circuit such as an invertercircuit formed with a thin film transistor, a capacitor, a resistor, andthe like. As an inverter circuit formed with a unipolar thin filmtransistor, there are a circuit formed by a combination of anenhancement-mode thin film transistor and a depletion-mode thin filmtransistor (hereinafter, referred to as an EDMOS circuit), a circuitformed by a combination of enhancement-mode thin film transistors(hereinafter, referred to as an EEMOS circuit), and an ERMOS circuit.Note that an n-channel thin film transistor with a positive thresholdvoltage is defined as an enhancement-mode transistor while an n-channelthin film transistor with a negative threshold voltage is defined as adepletion-mode transistor, and these definitions apply to thisspecification.

When an enhancement-mode transistor with a positive threshold voltage isused as a thin film transistor provided in the pixel portion, a currentflowing due to a voltage applied between a gate terminal and a sourceterminal can be made lower than that in the case of using adepletion-mode transistor, resulting in lower power consumption. It ispreferable that an enhancement-mode thin film transistor be also used asa thin film transistor in the driver circuit for driving the pixelportion as well as in the pixel portion. By using an enhancement-modethin film transistor as a thin film transistor of an inverter circuit,the pixel portion and the driver circuit can be manufactured with onekind of transistor, which makes it possible to reduce the number ofmanufacturing steps. Note that an enhancement-mode transistor uses anoxide semiconductor and has such electric characteristics as an on/offratio of 10⁹ or more at a gate voltage of −20 V to 20 V. Accordingly, asmall leakage current flows between a source terminal and a drainterminal, which allows low power consumption driving.

Note that in this document (specification, claims, drawings, and thelike), a thin film containing a compound represented by InMO₃ (ZnO)_(m)(m>0) is formed as an oxide semiconductor and the thin film is used formanufacturing a semiconductor element. Note that M denotes one or moreof metal elements selected from gallium (Ga), iron (Fe), nickel (Ni),manganese (Mn), and cobalt (Co). For example, M is gallium (Ga) in somecases, and in other cases, M contains other metal elements in additionto gallium (Ga), such as gallium (Ga) and nickel (Ni) or gallium (Ga)and iron (Fe). Furthermore, the above oxide semiconductor may contain atransition metal element such as iron (Fe) or nickel (Ni) or an oxide ofthe transition metal as an impurity element in addition to a metalelement contained as M. In addition, the concentration of sodium (Na)contained in the above oxide semiconductor is 5×10¹⁸ atoms/cm³ or less,preferably 1×10¹⁸ atoms/cm³ or less. In this document (specification,claims, drawings, and the like), this thin film is also referred to asan In—Ga—Zn—O-based non-single-crystal film.

Table 1 shows a typical example of measurement by inductively coupledplasma mass spectrometry (ICP-MS). An oxide semiconductor film ofInGa_(0.94)Zn_(0.40)O_(3.31) is obtained under Condition 1: a targetincluding In₂O₃, Ga₂O₃, and ZnO at a molar ratio of 1:1:1(In:Ga:Zn=1:1:0.5) is used, pressure is 0.4 Pa, direct current (DC)power source is 500 W, the flow rate of argon gas is 10 sccm, and theflow rate of oxygen gas is 5 sccm. Further, an oxide semiconductor filmof InGa_(0.95)Zn_(0.41)O_(3.33) is obtained under Condition 2 that isdifferent from Condition 1 only in the deposition atmosphere in whichthe flow rate of argon gas is changed to 40 sccm and the flow rate ofoxygen gas is changed to 0 sccm.

TABLE 1 flow rate concentrations (atomic %) Ar/O₂ In Ga Zn Oconcentration formula 10/5 17.7 16.7 7 58.6 InGa_(0.94)Zn_(0.40)O_(3.31)40/0 17.6 16.7 7.2 58.6 InGa_(0.95)Zn_(0.41)O_(3.33)

In addition, the measurement is performed by Rutherford backscatteringspectrometry (RBS) instead of ICP-MS, and the quantified results areshown in Table 2.

TABLE 2 flow rate concentrations (atomic %) Ar/O₂ In Ga Zn O Arconcentration formula 10/5 16 14.7 7.2 61.7 0.4InGa_(0.92)Zn_(0.45)O_(3.86) 40/0 17 15.8 7.5 59.4 0.3InGa_(0.93)Zn_(0.44)O_(3.49)

As the result of measurement of the sample in Condition 1 by RBS, anoxide semiconductor film of InGa_(0.92)Zn_(0.45)O_(3.86) is obtained.Further, as the result of measurement of the sample in Condition 2 byRBS, an oxide semiconductor film of InGa_(0.93)Zn_(0.44)O_(3.49) isobtained.

Even when an In—Ga—Zn—O-based non-single-crystal film is deposited bysputtering and then subjected to heat treatment at a temperature of 200°C. to 500° C., typically 300° C. to 400° C. for 10 minutes to 100minutes, an amorphous structure is observed when its crystal structureis analyzed by X-ray diffraction (XRD). In addition, it is possible tomanufacture a thin film transistor having such electric characteristicsas an on/off ratio of 10⁹ or more and a mobility of 10 or more at a gatevoltage of −20 V to 20 V. A thin film transistor manufactured using anoxide semiconductor layer having such electric characteristics has ahigher mobility than a thin film transistor manufactured using amorphoussilicon, which allows a driver circuit including a shift register to bedriven at high speed.

Next, an example of a circuit diagram of a gate line driver circuit anda source line driver circuit using an ERMOS circuit will be illustratedand described.

First, a structure of a source line driver circuit which uses an ERMOScircuit as an inverter circuit will be described.

FIG. 2 is a diagram illustrating a structure of the source line drivercircuit 101 included in the display device illustrated in FIG. 1. Thesource line driver circuit includes a clock signal level shifter 201, astart pulse level shifter 202, a pulse output circuit 203 which forms ashift register 251, a NAND circuit 204, a buffer 205, and a samplingswitch 206. Signals input from the outside are a first clock signal(CLK1), a second clock signal (CLK2), a start pulse (SP), and an analogvideo signal (Video). Among the signals input from the outside, theamplitude of the first clock signal (CLK1), the second clock signal(CLK2), and the start pulse (SP) is converted by the clock signal levelshifter 201 or the start pulse level shifter 202 immediately after theyhave been input from the outside as signals with low voltage amplitude,and then the signals are input to the driver circuit as signals withhigh voltage amplitude.

Further, in the source line driver circuit in the display device of thisembodiment, a sampling pulse which is output from a pulse output circuitof one stage in the shift register drives the sampling switch 206 tosample analog video signals of 12 source signal lines at the same time.Note that another signal for switching a scanning direction, or the likemay be additionally input. Although this embodiment shows an example inwhich clock signals having two phases, such as a first clock signal(CLK1) and a second clock signal (CLK2), are used for driving the drivercircuit, another structure may be employed in which signals other thanthe clock signals having two phases are input to drive the drivercircuit.

FIGS. 3A and 3B illustrate a structure of the plurality of pulse outputcircuits 203 included in the shift register 251. A pulse output circuit300 includes a first switch 301 connected to a terminal to which a startpulse SP is input; a first inverter circuit 302 that inverts a signalinput through the first switch 301 and outputs the inverted signal; asecond inverter circuit 303 and a third inverter circuit 305 that inverta signal output from the first inverter circuit 302 and output theinverted signal; and a second switch 304 connected to a terminal towhich a signal output from the second inverter circuit 303 is input.

In the circuit diagram illustrated in FIG. 3A, a block indicated by adotted line corresponds to a pulse output circuit 350 that outputs asampling pulse for one stage. The shift register in FIG. 3A includesN-stage (N is a natural number) pulse output circuits. Output signalsout1 to outN are output from an output terminal of the third invertercircuit 305 in each of the N-stage pulse output circuits. Note that inthe pulse output circuit of the second stage, which is next to theaforementioned first stage, a wiring to which the first clock signal isinput and a wiring to which the second clock signal is input areconnected to the second switch 304 and the first switch 301,respectively. That is, the connection in the second stage is changedfrom that in the first stage between the first switch 301 and the secondswitch 304. In the third stage and thereafter, the connection of thewirings to which the first clock signal and the second clock signal areinput is alternately switched between the first switch 301 and thesecond switch 304.

FIG. 3B illustrates in detail a circuit structure of the pulse outputcircuit. The pulse output circuit body includes thin film transistors351, 353, 355, 356, and 358, and resistors 352, 354, and 357. A pulseoutput circuit 331 of an odd-numbered stage and a pulse output circuit332 of an even-numbered stage are connected to a wiring 359 forsupplying the first clock signal (CLK1) and a wiring 360 for supplyingthe second clock signal (CLK2). Hereinafter, connection relationship ofa semiconductor element will be specifically described using the pulseoutput circuit 331 of the first stage as an example.

A first terminal of the thin film transistor 351 is connected to aterminal to which a start pulse SP is input, and a gate terminal of thethin film transistor 351 is connected to the wiring 359.

One terminal of the resistor 352 is connected to a wiring to which ahigh power supply potential VDD is supplied (also referred to as a highpotential line).

A first terminal of the thin film transistor 353 is connected to theother terminal of the resistor 352, a gate terminal of the thin filmtransistor 353 is connected to a second terminal of the thin filmtransistor 351, and a second terminal of the thin film transistor 353 isconnected to a wiring to which a low power supply potential VSS issupplied (also referred to as a low potential line).

One terminal of the resistor 354 is connected to the high potentialline.

A first terminal of the thin film transistor 355 is connected to theother terminal of the resistor 354, a gate terminal of the thin filmtransistor 355 is connected to the other terminal of the resistor 352and the first terminal of the thin film transistor 353, and a secondterminal of the thin film transistor 355 is connected to the lowpotential line.

A first terminal of the thin film transistor 356 is connected to theother terminal of the resistor 354 and the first terminal of the thinfilm transistor 355, a gate terminal of the thin film transistor 356 isconnected to the wiring 360, and a second terminal of the thin filmtransistor 356 is connected to the second terminal of the thin filmtransistor 351 and the gate terminal of the thin film transistor 353.

One terminal of the resistor 357 is connected to the high potentialline, and the other terminal thereof is connected to a first terminal ofa thin film transistor 351 in the pulse output circuit 332 of the secondstage.

A first terminal of the thin film transistor 358 is connected to theother terminal of the resistor 357 and the first terminal of the thinfilm transistor 351 in the pulse output circuit 332 of the second stage,a gate terminal of the thin film transistor 358 is connected to theother terminal of the resistor 352, the first terminal of the thin filmtransistor 353, and the gate terminal of the thin film transistor 355,and a second terminal of the thin film transistor 358 is connected tothe low potential line.

The pulse output circuit of the second stage has the same structure asthat of the first stage except that the connection of the wiring 359 andthe connection of the wiring 360 are switched to each other. In thethird stage and thereafter, the pulse output circuit 331 of theodd-numbered stage and the pulse output circuit 332 of the even-numberedstage are connected in a manner similar to the pulse output circuit 331of the first stage and the pulse output circuit 332 of the second stage,respectively.

In FIG. 3B, the thin film transistor 351 corresponds to the first switch301 illustrated in FIG. 3A. The resistor 352 and the thin filmtransistor 353 correspond to the first inverter circuit 302 illustratedin FIG. 3A, and the first inverter circuit 302 is an ERMOS circuit. Theresistor 354 and the thin film transistor 355 correspond to the secondinverter circuit 303 illustrated in FIG. 3A, and the second invertercircuit 303 is an ERMOS circuit. The thin film transistor 356corresponds to the second switch 304 illustrated in FIG. 3A. Theresistor 357 and the thin film transistor 358 correspond to the thirdinverter circuit 305 illustrated in FIG. 3A, and the third invertercircuit 305 is an ERMOS circuit.

It is preferable that the thin film transistors 351 and 356 beenhancement-mode transistors like the thin film transistors 353, 355,and 358. By using an enhancement-mode transistor as a switch, theoff-current of the transistor can be reduced, resulting in lower powerconsumption and reduction in the number of manufacturing steps.

Here, operation of the circuits illustrated in FIGS. 3A and 3B will bedescribed with reference to a timing chart of FIG. 4. Note that fordescription of FIG. 4, as the nodes in the pulse output circuit of thefirst stage illustrated in FIG. 3B, the second terminal of the thin filmtransistor 351 is referred to as a node A (denoted as A in FIG. 3B andFIG. 4), the other terminal of the resistor 352 is referred to as a nodeB (denoted as B in FIG. 3B and FIG. 4), the other terminal of theresistor 354 is referred to as a node C (denoted as C in FIG. 3B andFIG. 4), and the other terminal of the resistor 357 is referred to as anode out1 (denoted as out1 in FIG. 3B and FIG. 4).

In addition, as the nodes in the pulse output circuit of the secondstage illustrated in FIG. 3B, the second terminal of the thin filmtransistor 351 is referred to as a node D (denoted as D in FIG. 3B andFIG. 4), the other terminal of the resistor 352 is referred to as a nodeE (denoted as E in FIG. 3B and FIG. 4), the other terminal of theresistor 354 is referred to as a node F (denoted as F in FIG. 3B andFIG. 4), and the other terminal of the resistor 357 is referred to as anode out2 (denoted as out2 in FIG. 3B and FIG. 4). Furthermore, as thenodes in the pulse output circuit of the third stage illustrated in FIG.3B, the second terminal of the thin film transistor 351 is referred toas a node G (denoted as G in FIG. 3B and FIG. 4).

Operation in a period T1 in FIG. 4 will be described in which the startpulse SP is at H level, the first clock signal (CLK1) is at H level, andthe second clock signal (CLK2) is at L level.

When the first clock signal (CLK1) becomes H level, the thin filmtransistor 351 in the pulse output circuit of the first stage is turnedon.

Then, the voltage at the node A rises to H level due to the start pulseat H level.

When the voltage at the node A rises to H level, the thin filmtransistor 353 in the pulse output circuit of the first stage is turnedon.

Then, the voltage at the node B drops to L level due to the low powersupply potential at L level.

When the voltage at the node B drops to L level, the thin filmtransistor 355 and the thin film transistor 358 in the pulse outputcircuit of the first stage are turned off.

When the thin film transistor 355 in the pulse output circuit of thefirst stage is turned off, the voltage at the node C rises to H leveldue to the high power supply potential at H level. Moreover, when thethin film transistor 358 in the pulse output circuit of the first stageis turned off, the voltage at the node out1 rises to H level due to thehigh power supply potential at H level.

Note that since the second clock signal (CLK2) is at L level, the thinfilm transistor 356 in the pulse output circuit of the first stage andthe thin film transistor 351 in the pulse output circuit of the secondstage are turned off.

Next, operation in a period T2 in FIG. 4 will be described in which thestart pulse SP is at L level, the first clock signal (CLK1) is at Llevel, and the second clock signal is at H level.

When the first clock signal becomes L level, the thin film transistor351 in the pulse output circuit of the first stage is turned off. On theother hand, the thin film transistor 356 in the pulse output circuit ofthe first stage is turned on because the second clock signal (CLK2) isat H level. Accordingly, the voltage at the node A is kept at H leveldue to the voltage at the node C which is at H level in the period T1.

Thus, each of the nodes in the pulse output circuit of the first stageis kept at the same level as in the period T1.

On the other hand, since the second clock signal (CLK2) retains H level,the thin film transistor 351 in the pulse output circuit of the secondstage is turned on.

Then, the voltage at the node D rises to H level due to the voltage atthe node out1 which is at H level.

When the voltage at the node D rises to H level, the thin filmtransistor 353 in the pulse output circuit of the second stage is turnedon.

Then, the voltage at the node E drops to L level due to the low powersupply potential at L level.

When the voltage at the node E drops to L level, the thin filmtransistor 355 and the thin film transistor 358 in the pulse outputcircuit of the second stage are turned off.

When the thin film transistor 355 in the pulse output circuit of thesecond stage is turned off, the voltage at the node F rises to H leveldue to the high power supply potential at H level. Moreover, when thethin film transistor 358 in the pulse output circuit of the second stageis turned off, the voltage at the node out2 rises to H level due to thehigh power supply potential at H level.

Note that since the first clock signal (CLK1) is at L level, the thinfilm transistor 356 in the pulse output circuit of the second stage andthe thin film transistor 351 in the pulse output circuit of the thirdstage are turned off.

Next, operation in a period T3 in FIG. 4 will be described in which thestart pulse SP is at L level, the first clock signal (CLK1) is at Hlevel, and the second clock signal is at L level.

When the first clock signal retains H level, the thin film transistor351 in the pulse output circuit of the first stage is turned on. On theother hand, the thin film transistor 356 in the pulse output circuit ofthe first stage is turned off due to the second clock signal (CLK2) at Llevel. Accordingly, the voltage at the node A drops to L level.

When the voltage at the node A drops to L level, the thin filmtransistor 353 in the pulse output circuit of the first stage is turnedoff.

Then, the voltage at the node B rises to H level due to the high powersupply potential at H level.

When the voltage at the node B rises to H level, the thin filmtransistor 355 and the thin film transistor 358 in the pulse outputcircuit of the first stage are turned off.

When the thin film transistor 355 in the pulse output circuit of thefirst stage is turned on, the voltage at the node C drops to L level dueto the low power supply potential at L level. Moreover, when the thinfilm transistor 358 in the pulse output circuit of the first stage isturned on, the voltage at the node out1 drops to L level due to the lowpower supply potential at L level.

Note that since the second clock signal (CLK2) is at L level, the thinfilm transistor 356 in the pulse output circuit of the first stage isturned off.

Furthermore, as in the pulse output circuit of the first stage in theperiod T2, the thin film transistor 351 in the pulse output circuit ofthe second stage is turned off due to the second clock signal at Llevel. On the other hand, the first clock signal (CLK1) is at H level;thus, the thin film transistor 356 in the pulse output circuit of thesecond stage is turned on. Accordingly, the voltage at the node D iskept at H level due to the voltage at the node F which is at H level inthe period T2.

Thus, each of the nodes in the pulse output circuit of the second stageis kept at the same level as in the period T2.

On the other hand, when the first clock signal (CLK1) retains H level,the thin film transistor 351 in the pulse output circuit of the thirdstage is turned on.

Then, the voltage at the node G rises to H level due to the voltage atthe node out2 which is at H level.

When the voltage at the node G rises to H level, the thin filmtransistor 353 in the pulse output circuit of the third stage is turnedon.

Subsequently, the transistors are controlled to be on or off insequence, whereby the circuit illustrated in FIGS. 3A and 3B can operateas a shift register.

Note that in the pulse output circuit illustrated in FIGS. 3A and 3B,the thin film transistor 356 (the second switch 304) is provided betweenthe node A and the node C. This structure is adopted in consideration ofthe voltage drop at the node C from the high power supply potential VDDdue to the resistor 354. It is preferable that the node A and the node Cbe disconnected from each other to be independently driven by the thinfilm transistor 356 (the second switch 304), because the thin filmtransistor 353 can be driven more efficiently by the potential at thenode A. Note that the circuit of this embodiment can be driven withoutthe thin film transistor 356 (the second switch 304).

In addition, in the source line driver circuit, a NAND of a signaloutput from each pulse output circuit is calculated to generate a signalfor driving each source line. Accordingly, in the source line drivercircuit, a larger number of pulse output circuits than source lines arepreferably provided to generate a signal output to a source line.

FIG. 5A illustrates an example of a structure of the clock signal levelshifter 201 illustrated in FIG. 2. Note that since the first clocksignal (CLK1) level shifter and the second clock signal (CLK2) levelshifter have the same structure, FIG. 5A illustrates only the firstclock signal (CLK1) level shifter. FIG. 5A shows a structure in whichthe amplitude of the first clock signal (CLK1) is converted by an ERMOScircuit (Stage 1), and buffer stages (Stage 2 and Stage 3) aresubsequently provided.

Operation of the circuit illustrated in FIG. 5A is described. It isassumed here that three potentials of VSS, VDD0, and VDD are used andVSS<VDD0<VDD is satisfied. By employing a structure in which theamplitude of the first clock signal (CLK1) is level-shifted in an inputportion of a source line driver circuit, low power consumption andreduction in noise can be achieved.

A first input clock signal (CLK1) having an amplitude of L level/Hlevel=VSS/VDD0 is input to a signal input portion (CLK in1).

When the first input clock signal is at H level, a thin film transistor602 is turned on. Here, the on-resistance of the thin film transistor602 is set much lower than the resistance of a resistor 601. Thus, anode α becomes L level.

When the node α is at L level, a thin film transistor 604 is turned off.Here, the off-resistance of the thin film transistor 604 is set muchhigher than the resistance of a resistor 603. Thus, a node β becomes Hlevel, and the H level becomes substantially equal to VDD. As a result,amplitude conversion is completed.

In the level shifter illustrated in FIG. 5A, the buffer stages (Stage 2and Stage 3) are provided after the level shifter circuit (Stage 1) inconsideration of load of pulses after amplitude conversion. Operation isperformed similarly in the Stage 2 and the Stage 3, whereby a pulse isfinally output to a signal output portion.

FIG. 5A illustrates the first clock signal (CLK1) level shifter, and thestart pulse (SP) level shifter has the same structure.

FIG. 5B shows the conversion of the amplitude of a clock signal. Theamplitude of an input signal is L level/H level=VSS/VDD0, and theamplitude of an output signal is L level/H level=VSS/VDD.

FIG. 5C shows the conversion of the amplitude of a start pulse (SP).Like the clock signal, the amplitude of an input signal is L level/Hlevel=VSS/VDD0, and the amplitude of an output signal is L level/Hlevel=VSS/VDD.

FIG. 6A illustrates the NAND circuit 204 having two inputs illustratedin FIG. 2. The NAND circuit 204 has a structure similar to that of theERMOS circuit. In specific, the NAND circuit is different from the ERMOScircuit only in that signals are input to two input portions and thinfilm transistors 702 and 703 are connected in series.

When an H-level signal is input to a signal input portion (In1) and asignal input portion (In2), the thin film transistors 702 and 703 areturned on, whereby an L-level signal is output to a signal outputportion (Out).

On the other hand, when an L-level signal is input to one or both of thesignal input portion (In1) and the signal input portion (In2), anH-level signal having a potential of VDD is output to the signal outputportion (Out).

FIG. 6B illustrates the buffer 205 illustrated in FIG. 2. The buffer 205includes ERMOS circuits (Stage 1 to Stage 4). The operation of the ERMOScircuits is described in the above description on the level shiftercircuit, and thus the above description applies here.

FIG. 6C illustrates the sampling switch 206 illustrated in FIG. 2. Inthe sampling switch 206, a sampling pulse is input to a signal inputportion (25) so that 12 thin film transistors 731 connected in parallelare simultaneously controlled. An analog video signal is input to inputelectrodes (1) to (12) of the 12 thin film transistors 731, whereby thepotential of a video signal at the time of input of the sampling pulseis written to a source signal line.

FIG. 7 illustrates a structure of the gate line driver circuit in thedisplay device illustrated in FIG. 1. The gate line driver circuitincludes a clock signal level shifter 751, a start pulse level shifter752, a pulse output circuit 753 forming a shift register 781, a NANDcircuit 754, and a buffer 755.

A first clock signal (CLK1), a second clock signal (CLK2), and a startpulse (SP) are input to the gate line driver circuit. The amplitude ofthese input signals is converted by the clock signal level shifter 751or the start pulse level shifter 752 immediately after they have beeninput from the outside as signals with low voltage amplitude, and thenthe signals are input to the driver circuit as signals with high voltageamplitude.

Note that the structure and operation of the clock signal level shifter751, the start pulse level shifter 752, the pulse output circuit 753,the NAND circuit 754, and the buffer 755 are similar to those used inthe source line driver circuit, and thus the above description applieshere.

Next, FIG. 8 to FIG. 10 illustrate examples of a layout of the pulseoutput circuit illustrated in FIG. 3B. Note that FIG. 8 to FIG. 10illustrate the pulse output circuit of the first stage among themulti-stage pulse output circuits.

The pulse output circuit illustrated in FIG. 8 to FIG. 10 includes apower supply line 801, a power supply line 802, a control signal line803, a control signal line 804, a control signal line 805, thin filmtransistors 351, 353, 355, 356, and 358, and resistors 352, 354, and357.

FIG. 8 to FIG. 10 illustrate an oxide semiconductor layer 806, a firstwiring layer 807, a second wiring layer 808, and a contact hole 809.Note that the first wiring layer 807 is a layer including a gateterminal of a thin film transistor, and a second wiring layer 808 is alayer including a source terminal and a drain terminal (a first terminaland a second terminal) of a thin film transistor.

The connection relationship of each circuit element in FIG. 8 to FIG. 10is similar to that in FIG. 3B. That is, the power supply line 801 is awiring to which a high power supply potential VDD is supplied (alsoreferred to as a high potential line), the power supply line 802 is awiring to which a low power supply potential VSS is supplied (alsoreferred to as a low potential line), the control signal line 803 is awiring to which a start pulse (SP) is supplied, the control signal line804 is a wiring to which a first clock signal is supplied, and thecontrol signal line 805 is a wiring to which a second clock signal issupplied.

An oxide semiconductor layer with a rectangular shape is used for theresistors 352, 354, and 357 in the ERMOS circuit illustrated in FIG. 8.Therefore, the resistors 352, 354, and 357 illustrated in FIG. 8 have awide current path and high current driving capability. An oxidesemiconductor layer with a meander shape is used for the resistors 352,354, and 357 in the ERMOS circuit illustrated in FIG. 9 and FIG. 10. Theuse of the oxide semiconductor layer with a meander shape can increasethe resistance of the resistors 352, 354, and 357.

Note that in each layout of the pulse output circuits illustrated inFIG. 8 to FIG. 10, the thin film transistors 351, 353, 355, 356, and 358may have a channel region with a U shape. Although the thin filmtransistors have the same size in FIG. 8, the size of the thin filmtransistors may be changed as appropriate depending on the amount ofload of a subsequent stage.

Next, a structure of an inverter circuit including the resistor 354 andthe thin film transistor 355 illustrated in the layouts of FIG. 8 toFIG. 10 will be described with reference to FIGS. 11A to 11C. Note thatFIGS. 11A to 11C illustrate cross-sectional views of the resistor 354and the thin film transistor 355, which are taken along a dotted lineA-B and a dotted line C-D in FIG. 8 to FIG. 10.

FIG. 11A is a cross-sectional view taken along the dotted lines A-B andC-D in FIG. 8. In FIG. 11A, a first oxide semiconductor layer 905 isused for a resistor element of the resistor 354. One terminal of thefirst oxide semiconductor layer 905 is connected to a first wiring 901included in the first wiring layer 807 through a contact hole 904provided in an insulating layer 903, and the other terminal of the firstoxide semiconductor layer 905 is connected to a second wiring 907included in the second wiring layer 808.

In FIG. 11A, the thin film transistor 355 includes a gate terminal 902over a substrate, the insulating layer 903 over the gate terminal 902,which serves as a gate insulating layer, a second oxide semiconductorlayer 906 over the insulating layer 903, which is to be a channelformation region, and the second wiring 907 and a third wiring 908 overthe second oxide semiconductor layer 906, which serve as a sourceterminal and a drain terminal (a first terminal and a second terminal).

Note that the first wiring 901 serves as one terminal of the resistor354. The second wiring 907 serves as the other terminal of the resistor354 and one terminal of the thin film transistor 355, as well as awiring for connecting the resistor 354 and the thin film transistor 355.Similarly, the third wiring 908 serves as the second terminal of thethin film transistor 355 as well as a wiring to which a low power supplypotential VSS is supplied (also referred to as a low potential line). Inother words, the connecting wiring and the low (high) power supplypotential line are partly used as the first terminal or the secondterminal of each thin film transistor.

In FIG. 11A, the thicknesses of the first oxide semiconductor layer 905and the second oxide semiconductor layer 906 are not even. In specific,the first oxide semiconductor layer 905 and the second oxidesemiconductor layer 906 in a region overlapping the second wiring 907and the third wiring 908 have a thickness larger than that of the firstoxide semiconductor layer 905 and the second oxide semiconductor layer906 in the other region. This is because the first oxide semiconductorlayer 905 and the second oxide semiconductor layer 906 are partly etchedin etching for formation of the second wiring 907 and the third wiring908.

FIG. 11B is a cross-sectional view taken along the dotted lines A-B andC-D in FIG. 9. In FIG. 11B, the first oxide semiconductor layer 905formed in a meander shape is used for a resistor element of the resistor354. One terminal of the first oxide semiconductor layer 905 isconnected to the first wiring 901 through the contact hole 904 providedin the insulating layer 903, and the other terminal of the first oxidesemiconductor layer 905 is connected to the second wiring 907. Since thestructure of the thin film transistor is the same as that illustrated inFIG. 11A, the above description applies here.

FIG. 11C is a cross-sectional view taken along the dotted lines A-B andC-D in FIG. 10. In FIG. 11C, the first oxide semiconductor layer 905formed in a meander shape is used for a resistor element of the resistor354. One terminal of the first oxide semiconductor layer 905 isconnected to a fourth wiring 912 included in the second wiring layer808, and the other terminal of the first oxide semiconductor layer 905is connected to the second wiring 907 included in the second wiringlayer 808. Since the structure of the thin film transistor is the sameas that illustrated in FIG. 11A, the above description applies here. Inthe resistor 354 illustrated in FIG. 11C, the fourth wiring 912 isformed on and in direct contact with the first oxide semiconductor layer905; accordingly, a good contact can be made between the first oxidesemiconductor layer and the fourth wiring.

Next, materials of the ERMOS circuit illustrated in FIGS. 11A to 11Cwill be specifically described.

In FIGS. 11A to 11C, a glass substrate such as a barium borosilicateglass substrate or an aluminoborosilicate glass substrate can be used asa substrate 900. The first wiring 901 and the gate terminal 902 can bemade of a low-resistant conductive material such as aluminum (Al) orcopper (Cu). Alternatively, the first wiring 901 and the gate terminal902 may be formed of aluminum (Al) in combination with a heat-resistantconductive material. As the heat-resistant conductive material, it ispossible to use an element selected from titanium (Ti), tantalum (Ta),tungsten (W), molybdenum (Mo), chromium (Cr), neodymium (Nd), andscandium (Sc), an alloy containing any of the elements, an alloy filmcombining the elements, or a nitride containing any of the elements.

The insulating layer 903 can be made of an insulating film such as asilicon oxide film, a silicon nitride film, a silicon oxynitride film, asilicon nitride oxide film, an aluminum oxide film, or a tantalum oxidefilm. The insulating layer 903 may have a multi-layer structure of theseinsulating films. Note that the silicon oxynitride film refers to a filmwhich contains more oxygen than nitrogen and contains oxygen, nitrogen,silicon, and hydrogen at given concentrations ranging from 55 to 65atomic %, 1 to 20 atomic %, 25 to 35 atomic %, and 0.1 to 10 atomic %,respectively, where the total percentage of atoms is 100 atomic %.Further, the silicon nitride oxide film refers to a film which containsmore nitrogen than oxygen and contains oxygen, nitrogen, silicon, andhydrogen at given concentrations ranging from 15 to 30 atomic %, 20 to35 atomic %, 25 to 35 atomic %, and 15 to 25 atomic %, respectively,where the total percentage of atoms is 100 atomic %.

The first oxide semiconductor layer 905 and the second oxidesemiconductor layer 906 are made of a thin film containing a compoundrepresented by InMO₃(ZnO)_(m) (m>0). Note that M denotes one or more ofmetal elements selected from gallium (Ga), iron (Fe), nickel (Ni),manganese (Mn), and cobalt (Co). For example, M is gallium (Ga) in somecases, and in other cases, M contains other metal elements in additionto gallium (Ga), such as gallium (Ga) and nickel (Ni) or gallium (Ga)and iron (Fe). Furthermore, the above oxide semiconductor layer maycontain a transition metal element such as iron (Fe) or nickel (Ni) oran oxide of the transition metal as an impurity element in addition to ametal element contained as M. In addition, the concentration of sodium(Na) contained in the above oxide semiconductor layer is 5×10¹⁸atoms/cm³ or less, preferably 1×10¹⁸ atoms/cm³ or less.

As the material of the second wiring 907 and the third wiring 908, it ispossible to use an element selected from aluminum (Al), chromium (Cr),tantalum (Ta), titanium (Ti), molybdenum (Mo), and tungsten (W), analloy containing any of the elements, an alloy film combining theelements, or the like. The second wiring 907 and the third wiring 908may have a multi-layer structure of these elements.

A silicon oxide layer 909 is made of a silicon oxide film deposited bysputtering. A silicon nitride layer 910 deposited over the entiresurface of the substrate is formed by plasma CVD using a gas containinga hydrogen compound such as silane (SiH₄) and ammonia (NH₃).Accordingly, the silicon nitride layer 910 contains a high concentrationof hydrogen.

In addition, as illustrated in FIG. 12A, buffer layers 911 a to 911 cmay be provided between the first oxide semiconductor layer 905 and thesecond oxide semiconductor layer 906, and the second wiring 907 and thethird wiring 908.

Note that the buffer layers 911 a to 911 c are oxide semiconductorlayers having a low resistance, which are formed using anIn—Ga—Zn—O-based non-single-crystal film deposited under conditionsdifferent from those under which the first oxide semiconductor layer 905and the second oxide semiconductor layer 906 are formed. In thedescription below, for convenience, an oxide semiconductor film forforming the first oxide semiconductor layer 905 and the second oxidesemiconductor layer 906 is referred to as a first oxide semiconductorfilm, and an oxide semiconductor film for forming the buffer layers 911a to 911 c is referred to as a second oxide semiconductor film.

For example, in the case where an oxide semiconductor film is depositedby sputtering, the resistance of the oxide semiconductor film can bechanged by changing the oxygen concentration in a sputtering gas usedfor the deposition. In specific, the resistance of the oxidesemiconductor film can be increased by increasing the oxygenconcentration in a sputtering gas. One of the conditions for depositingthe first oxide semiconductor film and the second oxide semiconductorfilm by sputtering is as follows: a sputtering gas containing an argongas at a flow rate of 10 sccm and an oxygen gas at a flow rate of 5 sccmis used for depositing the first oxide semiconductor film; and asputtering gas containing an argon gas at a flow rate of 40 sccm is usedfor depositing the second oxide semiconductor film. Note that the bufferlayers 911 a to 911 c have n-type conductivity and an activation energy(ΔE) of 0.1 eV or less. The buffer layers 911 a to 911 c formed using anIn—Ga—Zn—O-based non-single-crystal film include at least an amorphouscomponent. The buffer layers 911 a to 911 c include a crystal grain(nanocrystal) in the amorphous structure in some cases. The crystalgrain (nanocrystal) in the buffer layers 911 a to 911 c has a diameterof 1 nm to 10 nm, and typically about 2 nm to 4 nm.

By providing the buffer layers 911 a to 911 c having a lower resistancethan the first oxide semiconductor layer 905 and the second oxidesemiconductor layer 906, a better contact than a Schottky junction canbe made between the second wiring 907 that is a conductor and the firstoxide semiconductor layer 905, and between the second wiring 907 and thethird wiring 908 that are conductors, and the second oxide semiconductorlayer 906. As a result, thermally stable operation can be achieved.Furthermore, by providing the buffer layers 911 b and 911 c in the thinfilm transistor 355, good mobility can be maintained even at a highdrain voltage.

In addition, as illustrated in FIG. 12B, the buffer layers 911 a to 911c and buffer layers 911 d and 911 e may be provided above and below thefirst oxide semiconductor layer 905 and the second oxide semiconductorlayer 906.

By providing the buffer layer 911 d, a better contact than a Schottkyjunction can be made between the first wiring 901 that is a conductorand the first oxide semiconductor layer 905, and thermally stableoperation can be achieved.

Next, thin film transistors having a structure different from thoseillustrated in FIGS. 11A to 11C and FIGS. 12A and 12B will be describedwith reference to FIGS. 13A and 13B. Note that FIGS. 13A and 13Billustrate cross-sectional structures of the resistor and the thin filmtransistor, which are taken along the dotted line A-B and the dottedline C-D in FIG. 8. In FIGS. 13A and 13B, the same components as inFIGS. 11A to 11C are denoted by the same reference numerals.

In FIG. 13A, a channel protective layer 1001 that is a silicon oxidelayer is provided over the second oxide semiconductor layer 906, and thesecond wiring 907 and the third wiring 908 are provided over the channelprotective layer 1001 and the second oxide semiconductor layer 906.Furthermore, the silicon nitride layer 910 is provided over the secondwiring 907, the third wiring 908, and the channel protective layer 1001.In addition, the buffer layers 911 a to 911 c may be provided betweenthe first oxide semiconductor layer 905 and the second oxidesemiconductor layer 906, and the second wiring 907 and the third wiring908 as illustrated in FIG. 13B.

Although an inverted staggered thin film transistor is shown in FIGS.11A to 11C, FIGS. 12A and 12B, and FIGS. 13A and 13B, the thin filmtransistor of this embodiment is not limited to the inverted staggeredthin film transistor. For example, the same effect can be obtained byusing a coplanar thin film transistor. Examples of a cross-sectionalstructure of the coplanar thin film transistor are illustrated in FIGS.14A and 14B and described. Note that FIGS. 14A and 14B illustratecross-sectional structures of the resistor and the thin film transistor,which are taken along the dotted line A-B and the dotted line C-D inFIG. 8. In FIGS. 14A and 14B, the same components as in FIGS. 11A to 11Care denoted by the same reference numerals.

In FIG. 14A, one end of the first oxide semiconductor layer 905 isprovided over the first wiring 901, the other end of the first oxidesemiconductor layer 905 and one end of the second oxide semiconductorlayer 906 are provided over the second wiring 907, and the other end ofthe second oxide semiconductor layer 906 is provided over the thirdwiring 908. Furthermore, the silicon oxide layer 909 and the siliconnitride layer 910 are stacked over the second oxide semiconductor layer906, and only the silicon nitride layer 910 is provided over the firstoxide semiconductor layer 905. In addition, as illustrated in FIG. 14B,buffer layers 1010 a and 1010 b may be provided between the secondwiring 907 and the third wiring 908, and the insulating layer 903.

In FIGS. 11A to 11C, FIGS. 12A and 12B, FIGS. 13A and 13B, and FIGS. 14Aand 14B, the silicon nitride layer 910 is formed in direct contact withthe first oxide semiconductor layer 905 by plasma CVD using a gascontaining a hydrogen compound such as silane (SiH₄) and ammonia (NH₃).

An ERMOS circuit having the aforementioned structure includes a resistorin which the first oxide semiconductor layer 905 on which the siliconnitride layer 910 is provided in direct contact therewith is used for aresistor element, and a thin film transistor in which the second oxidesemiconductor layer 906 over which the silicon nitride layer 910 isprovided with the silicon oxide layer 909 (the channel protective layer1001) interposed therebetween is used for a channel formation region.Accordingly, a higher concentration of hydrogen can be introduced intothe first oxide semiconductor layer 905 than into the second oxidesemiconductor layer 906. As a result, the resistance of the first oxidesemiconductor layer 905 can be made lower than that of the second oxidesemiconductor layer 906.

Next, a manufacturing process of the ERMOS circuit will be describedwith reference to cross-sectional views of FIGS. 15A to 15C. Note that amanufacturing process of the ERMOS circuit illustrated in FIG. 14B willbe described here.

A first conductive film is deposited over the substrate 900. The firstconductive film is deposited by a thin film deposition method typifiedby sputtering, vacuum evaporation, pulse laser deposition, ion plating,and the like. As the material of the first conductive film, alow-resistance conductive material such as aluminum (Al) or copper (Cu)can be used. Alternatively, the first conductive film may be formed ofaluminum (Al) in combination with a heat-resistant conductive material.As the heat-resistant conductive material, it is possible to use anelement selected from titanium (Ti), tantalum (Ta), tungsten (W),molybdenum (Mo), chromium (Cr), neodymium (Nd), and scandium (Sc), analloy containing any of the elements, an alloy film combining theelements, or a nitride containing any of the elements. Then, a resist isformed over the first conductive film by a first photolithography step.Furthermore, the first conductive film is selectively etched using theresist as a mask, thereby forming the first wiring 901 and the gateterminal 902.

Then, an insulating film is formed to cover the first wiring 901 and thegate terminal 902. The insulating film is deposited by a thin filmdeposition method typified by sputtering, vacuum evaporation, pulselaser deposition, ion plating, plasma CVD, and the like. The insulatingfilm can be made of an insulating film such as a silicon oxide film, asilicon nitride film, a silicon oxynitride film, a silicon nitride oxidefilm, an aluminum oxide film, or a tantalum oxide film. The insulatingfilm may have a multi-layer structure of these insulating films. Then, aresist is formed over the insulating film by a second photolithographystep. Furthermore, the insulating film is selectively etched using theresist as a mask, thereby forming the insulating layer 903 having thecontact hole 904 that reaches the first wiring. FIG. 15A is across-sectional view in which these steps have been completed.

Then, a second oxide semiconductor film is deposited. The second oxidesemiconductor film is deposited by a thin film deposition methodtypified by sputtering, vacuum evaporation, pulse laser deposition, ionplating, plasma CVD, and the like. In the case where the second oxidesemiconductor film is deposited by sputtering, it is preferable to use atarget made by sintering In₂O₃, Ga₂O₃, and ZnO. As a sputtering gas, arare gas typified by an argon gas is used. One of the depositionconditions by sputtering is as follows: a target made by mixing andsintering In₂O₃, Ga₂O₃, and ZnO (1:1:1) is used; pressure is 0.4 Pa;direct current (DC) power source is 500 W; and the flow rate of argongas is 40 sccm.

Then, a second conductive film is deposited. The second conductive filmis deposited by a thin film deposition method typified by sputtering,vacuum evaporation, pulse laser deposition, ion plating, and the like.As the material of the second conductive film, it is possible to use anelement selected from aluminum (Al), chromium (Cr), tantalum (Ta),titanium (Ti), molybdenum (Mo), and tungsten (W), an alloy containingany of the elements, an alloy film combining the elements, or the like.The second conductive film may have a multi-layer structure of theseelements.

Then, a resist is formed over the second conductive film by a thirdphotolithography step. Furthermore, the second oxide semiconductor filmand the second conductive film are selectively etched using the resistas a mask, thereby forming the second wiring 907, the third wiring 908,and the buffer layers 1010 a and 1010 b. This etching step is performedby wet etching or dry etching. For example, in the case where analuminum (Al) film or an aluminum alloy film is used as the secondconductive film, wet etching can be performed using a mixed solution ofphosphoric acid, acetic acid, and nitric acid. Similarly, in the casewhere a titanium (Ti) film or a titanium alloy film is used as thesecond conductive film, wet etching can be performed using an ammoniahydrogen peroxide mixture (hydrogen peroxide:ammonia:water=5:2:2).

Then, a first oxide semiconductor film is deposited. The first oxidesemiconductor film is deposited by a thin film deposition methodtypified by sputtering, vacuum evaporation, pulse laser deposition, ionplating, and the like. The first oxide semiconductor film is depositedunder the conditions in which a sputtering gas contains a higher oxygenconcentration than under the conditions for forming the second oxidesemiconductor film. One of the deposition conditions by sputtering is asfollows: a target made by mixing and sintering In₂O₃, Ga₂O₃, and ZnO(1:1:1) is used; pressure is 0.4 Pa; direct current (DC) power source is500 W; the flow rate of argon gas is 10 sccm; and the flow rate ofoxygen gas is 5 sccm.

Before depositing the first oxide semiconductor film, reverse sputteringwhere an argon gas is introduced to generate plasma is preferablyperformed, so that dust attached to the insulating layer 903, the firstwiring 901, the second wiring 907, and the third wiring 908 can beremoved. In addition, the reverse sputtering is preferably conducted inan atmosphere in which oxygen is added to argon, whereby the firstwiring 901, the second wiring 907, and the third wiring 908 that areconductors are oxidized, resulting in an increase in the resistance inthe vicinity of the interface with the second oxide semiconductor film.Thus, the off-current of a thin film transistor formed later can bereduced. Note that the reverse sputtering is a method in which voltageis applied to a substrate side in an argon atmosphere with the use of anRF power source without applying voltage to a target side, so thatplasma is generated to modify the surface of the substrate.

Then, a resist is formed over the first oxide semiconductor film by afourth photolithography step. Furthermore, the first oxide semiconductorfilm is selectively etched using the resist as a mask, thereby formingthe first oxide semiconductor layer 905 and the second oxidesemiconductor layer 906. FIG. 15B is a cross-sectional view in whichthese steps have been completed.

Then, a silicon oxide film is deposited by sputtering. For example, thesilicon oxide film can be deposited using silicon as a target and usinga sputtering gas containing argon and oxygen. Alternatively, the siliconoxide film can be deposited using silicon oxide as a target and usingargon as a sputtering gas. Subsequently, a resist is formed over thesilicon oxide film by a fifth photolithography step. Furthermore, thesilicon oxide film is selectively etched using the resist as a mask,thereby forming the silicon oxide layer 909 over the second oxidesemiconductor layer 906.

Then, the silicon nitride layer 910 serving as a passivation film isdeposited over the entire surface of the substrate. The silicon nitridelayer 910 is formed by plasma CVD using a gas containing a hydrogencompound such as silane (SiH₄) and ammonia (NH₃), and is a siliconnitride layer containing a high concentration of hydrogen.

Then, heat treatment is performed at 200° C. to 600° C., typically 250°C. to 500° C. For example, heat treatment is performed in a furnace in anitrogen atmosphere at 350° C. for one hour. FIG. 15C is across-sectional view in which these steps have been completed.

Through the above steps, the resistor 354 and the thin film transistor355 can be manufactured using the oxide semiconductor layers.

Note that the order of the steps described above is an example and thereis no particular limitation on the order. Manufacturing steps differentfrom those in FIGS. 15A to 15C are illustrated in FIGS. 16A to 16C anddescribed.

A first conductive film is deposited over the substrate 900. Then, aresist is formed over the first conductive film by a firstphotolithography step. Furthermore, the first conductive film isselectively etched using the resist as a mask, thereby forming the firstwiring 901 and the gate terminal 902.

Then, an insulating film is formed to cover the first wiring 901 and thegate terminal 902. After that, a second oxide semiconductor film isdeposited. Then, a second conductive film is deposited. Subsequently, aresist is formed over the second conductive film by a secondphotolithography step. Furthermore, the second conductive film and thesecond oxide semiconductor film are selectively etched using the resistas a mask, thereby forming the second wiring 907, the third wiring 908,and the buffer layers 1010 a and 1010 b. FIG. 16A is a cross-sectionalview in which these steps have been completed.

Then, a resist is formed over the insulating film by a thirdphotolithography step. Furthermore, the insulating film is selectivelyetched using the resist as a mask, thereby forming the insulating layer903 having the contact hole 904 that reaches the first wiring 901.

Then, a first oxide semiconductor film is deposited. After that, aresist is formed over the first oxide semiconductor film by a fourthphotolithography step. Furthermore, the first oxide semiconductor filmis selectively etched using the resist as a mask, thereby forming thefirst oxide semiconductor layer 905 and the second oxide semiconductorlayer 906. FIG. 16B is a cross-sectional view in which these steps havebeen completed.

Then, a silicon oxide film is deposited by sputtering. Subsequently, aresist is formed over the silicon oxide film by a fifth photolithographystep. Furthermore, the silicon oxide film is selectively etched usingthe resist as a mask, thereby forming the silicon oxide layer 909 tocover the second oxide semiconductor layer 906.

Then, the silicon nitride layer 910 serving as a passivation film isdeposited over the entire surface of the substrate by plasma CVD using agas containing a hydrogen compound such as silane (SiH₄) and ammonia(NH₃).

Then, heat treatment is performed at 200° C. to 600° C. in a nitrogenatmosphere. FIG. 16C is a cross-sectional view in which these steps havebeen completed.

Through the above steps, the resistor 354 and the thin film transistor355 can be manufactured using the oxide semiconductor layers. Inaddition, in the steps illustrated in FIGS. 16A to 16C, the first oxidesemiconductor film can be deposited after the contact hole 904 isformed. Therefore, the number of steps in which the bottom surface ofthe contact hole is exposed can be reduced, and the material of thefirst wiring 901 can be selected more freely.

The resistor and the thin film transistor described in this embodimentare formed using the oxide semiconductor layers. Accordingly, a drivercircuit including the resistor and the thin film transistor has gooddynamic characteristics. Moreover, the silicon nitride layer formed byplasma CVD using a gas containing a hydrogen compound such as silane(SiH₄) and ammonia (NH₃) is provided on and in direct contact with thefirst oxide semiconductor layer used for the resistor, and the siliconnitride layer is provided over the second oxide semiconductor layer usedfor the thin film transistor with the silicon oxide layer serving as abarrier layer interposed therebetween. Therefore, a higher concentrationof hydrogen is introduced into the first oxide semiconductor layer indirect contact with the silicon nitride layer containing a highconcentration of hydrogen than into the second oxide semiconductorlayer. As a result, the resistance of the first oxide semiconductorlayer can be made lower than that of the second oxide semiconductorlayer. Thus, the thin film transistor and the resistor do not need to bemanufactured in different steps, which makes it possible to provide adriver circuit manufactured in a smaller number of steps.

Embodiment 2

In this embodiment, another example of the resistor and the thin filmtransistor, which is different from that of Embodiment 1, will bedescribed with reference to FIG. 17. Note that FIG. 17 illustrates across-sectional structure of the resistor and the thin film transistor,which is taken along the dotted line A-B and the dotted line C-D in FIG.8 shown in Embodiment 1.

The first wiring 901 and the gate terminal 902 are provided over thesubstrate 900. Then, the insulating layer 903 is provided over the firstwiring 901 and the gate terminal 902. Note that the substrate 900, thefirst wiring 901, the gate terminal 902, and the insulating layer 903can be made of the materials described in Embodiment 1; thus, thedescription of Embodiment 1 applies in this embodiment.

A first oxide semiconductor layer 2001 containing a high concentrationof nitrogen and a second oxide semiconductor layer 2002 containing ahigh concentration of nitrogen are provided over the insulating layer903 so as to overlap the first wiring 901 and the gate terminal 902,respectively. Note that the first wiring 901 is in contact with thefirst oxide semiconductor layer 2001 containing a high concentration ofnitrogen through the contact hole 904 formed in the insulating layer903.

Note that the first oxide semiconductor layer 2001 containing a highconcentration of nitrogen and the second oxide semiconductor layer 2002containing a high concentration of nitrogen are oxide semiconductorlayers with a high concentration of nitrogen, which are formed of anoxide semiconductor film formed under conditions different from thoseunder which the first oxide semiconductor film and the second oxidesemiconductor film shown in Embodiment 1 are formed. In specific, thefirst oxide semiconductor layer 2001 and the second oxide semiconductorlayer 2002 each have a ratio of nitrogen (N) to oxygen (O) (N/O) of 0.05to 0.8, preferably 0.1 to 0.5.

For example, in the case where the oxide semiconductor film containing ahigh concentration of nitrogen is deposited by sputtering, depositionmay be performed using a sputtering gas containing a nitrogen gas. Oneof the deposition conditions by sputtering is as follows: a targetincluding In₂O₃, Ga₂O₃, and ZnO (1:1:1) (In:Ga:Zn=1:1:0.5) is used;pressure is 0.4 Pa; direct current (DC) power source is 500 W; the flowrate of argon gas is 35 sccm and the flow rate of nitrogen gas is 5sccm. Note that it is preferable to use a pulsed direct current (DC)power source so that dust can be reduced and thickness distribution canbe evened. Subsequently, the oxide semiconductor film containing a highconcentration of nitrogen is subjected to photolithography, therebyforming the first oxide semiconductor layer 2001 containing a highconcentration of nitrogen and the second oxide semiconductor layer 2002containing a high concentration of nitrogen.

Then, the second wiring 907 and the third wiring 908 are provided. Thesecond wiring 907 covers one end of the first oxide semiconductor layer2001 containing a high concentration of nitrogen and one end of thesecond oxide semiconductor layer 2002 containing a high concentration ofnitrogen, and the third wiring 908 covers the other end of the secondoxide semiconductor layer 2002 containing a high concentration ofnitrogen. Note that the second wiring 907 and the third wiring 908 canbe made of the materials described in Embodiment 1; thus, thedescription of Embodiment 1 applies in this embodiment.

Then, the silicon oxide layer 909 is provided over the second oxidesemiconductor layer 2002 containing a high concentration of nitrogen.The silicon oxide layer is formed by selectively etching a silicon oxidefilm which is deposited by sputtering. The silicon oxide film can bedeposited using silicon as a target and using a sputtering gascontaining argon and oxygen, or deposited using silicon oxide as atarget and using a sputtering gas containing argon.

At this time, heat treatment is performed at 200° C. to 600° C.,typically 250° C. to 500° C. in an atmosphere containing a substancewhich is a supply source of a hydrogen atom. For example, the heattreatment is performed at 350° C. for one hour. As the atmospherecontaining a substance which is a supply source of a hydrogen atom, amixed atmosphere of hydrogen and a rare gas such as argon can be used.

Nitrogen in the oxide semiconductor layer has the effect of preventingatoms forming the oxide semiconductor layer from tightly filling thefilm, and of promoting diffusion and solid dissolution of hydrogen inthe film. Accordingly, the heat treatment allows hydrogen to beintroduced into the first oxide semiconductor layer 2001 containing ahigh concentration of nitrogen. As a result, the concentration ofhydrogen in the first oxide semiconductor layer 2001 containing a highconcentration of nitrogen becomes higher than that in the second oxidesemiconductor layer 2002 containing a high concentration of nitrogen. Inother words, the resistance of the first oxide semiconductor layer 2001containing a high concentration of nitrogen can be made lower than thatof the second oxide semiconductor layer 2002 containing a highconcentration of nitrogen.

Furthermore, the silicon nitride layer 910 is formed over the entiresurface of the substrate by plasma CVD using a gas containing a hydrogencompound such as silane (SiH₄) and ammonia (NH₃). The silicon nitridelayer 910 is a silicon nitride layer containing a high concentration ofhydrogen. Accordingly, the concentration of hydrogen in the first oxidesemiconductor layer 2001 containing a high concentration of nitrogenthat is in direct contact with the silicon nitride layer 910 can befurther increased to reduce resistance.

Through the above steps, it is possible to form the resistor 354 usingthe first oxide semiconductor layer 2001 containing a high concentrationof nitrogen and having a low resistance and the thin film transistor 355using the second oxide semiconductor layer 2002 containing a highconcentration of nitrogen and having a high resistance.

Although the cross-sectional structure of the resistor corresponding tothe line A-B in FIG. 8 is shown in this embodiment, the first oxidesemiconductor layer containing a high concentration of nitrogen may havea meander shape as illustrated in FIG. 9 and FIG. 10. In addition, asillustrated in FIG. 10, the wiring layers may be formed over the bothends of the oxide semiconductor layer containing a high concentration ofnitrogen.

In this embodiment, the cross-sectional structure of the channel-etchedthin film transistor is shown; however, a channel-stop thin filmtransistor can also be used. Furthermore, although the invertedstaggered thin film transistor is shown in this embodiment, a coplanarthin film transistor can also be used.

The resistor and the thin film transistor shown in this embodiment areformed using the oxide semiconductor layer containing a highconcentration of nitrogen. Thus, a driver circuit including the resistorand the thin film transistor has good dynamic characteristics. Inaddition, since the heat treatment is performed at 200° C. to 600° C.,typically 250° C. to 500° C. in an atmosphere containing a substancewhich is a supply source of a hydrogen atom, hydrogen is introduced intothe first oxide semiconductor layer containing a high concentration ofnitrogen that is used for the resistor. Accordingly, a higherconcentration of hydrogen is introduced into the first oxidesemiconductor layer containing a high concentration of nitrogen thaninto the second oxide semiconductor layer containing a highconcentration of nitrogen. As a result, the resistance of the firstoxide semiconductor layer containing a high concentration of nitrogencan be made lower than that of the second oxide semiconductor layercontaining a high concentration of nitrogen. Thus, the thin filmtransistor and the resistor do not need to be manufactured in differentsteps, which makes it possible to provide a driver circuit manufacturedin a smaller number of steps.

Embodiment 3

In this embodiment, a resistor and a thin film transistor that aremanufactured using the oxide semiconductor layer described in Embodiment1 and the oxide semiconductor layer containing a high concentration ofnitrogen described in Embodiment 2 will be described with reference toFIGS. 18A to 18C and FIGS. 19A and 19B. Note that FIGS. 18A to 18C andFIGS. 19A and 19B illustrate cross-sectional structures of the resistorand the thin film transistor, which are taken along the dotted line A-Band the dotted line C-D in FIG. 8.

In this embodiment, specifically, a structure in which the oxidesemiconductor layer containing a high concentration of nitrogendescribed in Embodiment 2 is used instead of the buffer layers describedin Embodiment 1 will be described with reference to FIGS. 18A to 18C andFIGS. 19A and 19B.

First, a first conductive film is deposited over the substrate 900. Thefirst conductive film is deposited by a thin film deposition methodtypified by sputtering, vacuum evaporation, pulse laser deposition, ionplating, and the like. Then, a resist is formed over the firstconductive film by a first photolithography step. Furthermore, the firstconductive film is selectively etched using the resist as a mask,thereby forming the first wiring 901 and the gate terminal 902. Then, aninsulating film is formed to cover the first wiring 901 and the gateterminal 902. The insulating film is deposited by a thin film depositionmethod typified by sputtering, vacuum evaporation, pulse laserdeposition, ion plating, plasma CVD, and the like. Subsequently, aresist is formed over the insulating film by a second photolithographystep. Furthermore, the insulating film is selectively etched using theresist as a mask, thereby forming the insulating layer 903 having thecontact hole 904. Note that the first wiring 901, the gate terminal 902,and the insulating layer 903 can be made of the materials described inEmbodiment 1; thus, the description of Embodiment 1 applies in thisembodiment. FIG. 18A is a cross-sectional view in which these steps havebeen completed.

Then, an oxide semiconductor film 950 is deposited. The oxidesemiconductor film 950 is deposited by a thin film deposition methodtypified by sputtering, vacuum evaporation, pulse laser deposition, ionplating, plasma CVD, and the like. In the case where the oxidesemiconductor film 950 is deposited by sputtering, it is preferable touse a target made by sintering In₂O₃, Ga₂O₃, and ZnO. One of thedeposition conditions by sputtering is as follows: a target made bymixing and sintering In₂O₃, Ga₂O₃, and ZnO (1:1:1) is used; pressure is0.4 Pa; direct current (DC) power source is 500 W; the flow rate ofargon gas is 10 sccm; and the flow rate of oxygen gas is 5 sccm.

Then, an oxide semiconductor film 951 containing a high concentration ofnitrogen is deposited. The oxide semiconductor film 951 containing ahigh concentration of nitrogen is deposited by a thin film depositionmethod typified by sputtering, vacuum evaporation, pulse laserdeposition, ion plating, and the like. In the case where the oxidesemiconductor film 951 is deposited by sputtering, it is preferable touse a target made by sintering In₂O₃, Ga₂O₃, and ZnO. The oxidesemiconductor film 951 containing a high concentration of nitrogen isdeposited by sputtering, for example, under the following conditions: atarget made by mixing and sintering In₂O₃, Ga₂O₃, and ZnO (1:1:1) isused; pressure is 0.4 Pa; direct current (DC) power source is 500 W; theflow rate of argon gas is 35 sccm; and the flow rate of nitrogen gas is5 sccm. FIG. 18B is a cross-sectional view in which these steps havebeen completed.

Then, a resist is formed over the oxide semiconductor film 951containing a high concentration of nitrogen by a third photolithographystep. Furthermore, the oxide semiconductor film 950 and the oxidesemiconductor film 951 containing a high concentration of nitrogen areselectively etched using the resist as a mask, thereby forming a stackof a first oxide semiconductor layer 960 and a first oxide semiconductorlayer 961 containing a high concentration of nitrogen, and a stack of asecond oxide semiconductor layer 962 and a second oxide semiconductorlayer 963 containing a high concentration of nitrogen. FIG. 18C is across-sectional view in which these steps have been completed.

At this time, heat treatment is performed at 200° C. to 600° C.,typically 250° C. to 500° C. in an atmosphere containing a substancewhich is a supply source of a hydrogen atom. For example, the heattreatment is performed at 350° C. for one hour. As the atmospherecontaining a substance which is a supply source of a hydrogen atom, amixed atmosphere of hydrogen and a rare gas such as argon can be used.

Nitrogen in the oxide semiconductor layer has the effect of preventingatoms forming the oxide semiconductor layer from tightly filling thefilm, and of promoting diffusion and solid dissolution of hydrogen inthe film. Accordingly, the heat treatment allows hydrogen to beintroduced into the first oxide semiconductor layer 961 containing ahigh concentration of nitrogen and the second oxide semiconductor layer963 containing a high concentration of nitrogen. As a result, theresistance of the first oxide semiconductor layer 961 containing a highconcentration of nitrogen and the second oxide semiconductor layer 963containing a high concentration of nitrogen can be reduced.

Then, a second conductive film is deposited. The second conductive filmis deposited by a thin film deposition method typified by sputtering,vacuum evaporation, pulse laser deposition, ion plating, and the like.Then, a resist is formed over the second conductive film by a fourthphotolithography step. Furthermore, the second conductive film isselectively etched using the resist as a mask, thereby forming thesecond wiring 907 and the third wiring 908. Note that the second wiring907 and the third wiring 908 can be made of the materials described inEmbodiment 1; thus, the description of Embodiment 1 applies in thisembodiment. In this etching step, the oxide semiconductor layercontaining a high concentration of nitrogen in a region that does notoverlap the second wiring 907 and the third wiring 908 is etched to beremoved. In addition, part of the oxide semiconductor layer in thatregion is also etched to form oxide semiconductor layers 964 and 966 andoxide semiconductor layers 965, 967, and 968 containing a highconcentration of nitrogen. FIG. 19A is a cross-sectional view in whichthese steps have been completed.

Then, a silicon oxide film is deposited by sputtering. For example, thesilicon oxide film can be deposited using silicon as a target and usinga sputtering gas containing argon and oxygen. Alternatively, the siliconoxide film can be deposited using silicon oxide as a target and usingargon as a sputtering gas. Subsequently, a resist is formed over thesilicon oxide film by a fifth photolithography step. Furthermore, thesilicon oxide film is selectively etched using the resist as a mask,thereby forming the silicon oxide layer 909.

Then, the silicon nitride layer 910 serving as a passivation film isdeposited. The silicon nitride layer 910 is formed by plasma CVD using agas containing a hydrogen compound such as silane (SiH₄) and ammonia(NH₃). Through the above steps, the resistor 354 and the thin filmtransistor 355 are formed. FIG. 19B is a cross-sectional view in whichthese steps have been completed.

In the resistor 354 and the thin film transistor 355 shown in thisembodiment, the oxide semiconductor layers 965, 967, and 968 containinga high concentration of nitrogen, into which hydrogen is introduced andwhich have a low resistance, are formed between the oxide semiconductorlayers and the wiring layers that are conductors. Accordingly, a bettercontact than a Schottky junction can be made between the oxidesemiconductor layers and the wiring layers, and thermally stableoperation can be achieved. In addition, by providing the oxidesemiconductor layers 967 and 968 containing a high concentration ofnitrogen in the thin film transistor 355, good mobility can bemaintained even at a high drain voltage.

Note that the aforementioned manufacturing process shows an example inwhich heat treatment for introducing hydrogen into the oxidesemiconductor layer containing a high concentration of nitrogen isconducted after the etching step of the oxide semiconductor layer.However, the heat treatment may be conducted at any time afterdeposition of the oxide semiconductor film containing a highconcentration of nitrogen and before deposition of the second conductivefilm. For example, the heat treatment can be conducted in the subsequentstep of deposition of the oxide semiconductor film containing a highconcentration of nitrogen.

Although the cross-sectional structure of the resistor corresponding tothe line A-B in FIG. 8 is shown in this embodiment, the oxidesemiconductor layer may have a meander shape as illustrated in FIG. 9and FIG. 10. In addition, as illustrated in FIG. 10, the wiring layersmay be formed over the both ends of the oxide semiconductor layercontaining a high concentration of nitrogen.

In this embodiment, the cross-sectional structure of the channel-etchedthin film transistor is shown; however, a channel-stop thin filmtransistor can also be used. Furthermore, although the invertedstaggered thin film transistor is shown in this embodiment, a coplanarthin film transistor can also be used.

The resistor and the thin film transistor described in this embodimentare formed using the oxide semiconductor layer and the oxidesemiconductor layer containing a high concentration of nitrogen.Accordingly, a driver circuit including the resistor and the thin filmtransistor has good dynamic characteristics. Moreover, the siliconnitride layer formed by plasma CVD using a gas containing a hydrogencompound such as silane (SiH₄) and ammonia (NH₃) is provided on and indirect contact with the first oxide semiconductor layer used for theresistor, and the silicon nitride layer is provided over the secondoxide semiconductor layer used for the thin film transistor with thesilicon oxide layer serving as a barrier layer interposed therebetween.Therefore, a higher concentration of hydrogen is introduced into thefirst oxide semiconductor layer in direct contact with the siliconnitride layer containing a high concentration of hydrogen than into thesecond oxide semiconductor layer. As a result, the resistance of thefirst oxide semiconductor layer can be made lower than that of thesecond oxide semiconductor layer. Thus, the thin film transistor and theresistor do not need to be manufactured in different steps, which makesit possible to provide a driver circuit manufactured in a smaller numberof steps.

Embodiment 4

In this embodiment, an example of a structure of a driver circuitincluding a shift register formed by a dynamic circuit will be describedwith reference to FIGS. 20A to 20C.

A pulse output circuit 1400 illustrated in FIG. 20A includes an invertercircuit 1401 to which a start pulse (SP) is input from an inputterminal, a switch 1402 one terminal of which is connected to an outputterminal of the inverter circuit 1401, and a capacitor 1403 connected tothe other terminal of the switch 1402. Note that the switch 1402 in thepulse output circuit of an odd-numbered stage is controlled to be on oroff by a first clock signal (CLK1), and the switch 1402 in the pulseoutput circuit of an even-numbered stage is controlled to be on or offby a second clock signal (CLK2).

FIG. 20B illustrates in detail a circuit structure of the pulse outputcircuit. The pulse output circuit 1400 includes thin film transistors1411 and 1413, a resistor 1412, and a capacitor 1414. The pulse outputcircuit of the odd-numbered stage is connected to a wiring 1415 forsupplying the first clock signal (CLK1), and the pulse output circuit ofthe even-numbered stage is connected to a wiring 1416 for supplying thesecond clock signal (CLK2). In the pulse output circuit 1400, the thinfilm transistor 1411 and the resistor 1412 correspond to the invertercircuit 1401 illustrated in FIG. 20A, which is an ERMOS circuit. Thethin film transistor 1413 corresponds to the switch 1402 illustrated inFIG. 17A, and the capacitor 1414 corresponds to the capacitor 1403illustrated in FIG. 20A. It is preferable that the thin film transistor1413 be an enhancement-mode transistor like the thin film transistor1411. By using an enhancement-mode transistor as a switch, theoff-current of the transistor can be reduced, resulting in lower powerconsumption and reduction in the number of manufacturing steps.

FIG. 20C is a timing chart showing the circuit operation of the circuitsillustrated in FIGS. 20A and 20B. Note that in FIG. 20C, nodes in thecircuit of FIG. 20B are denoted as nodes A to E for description.

First, operation will be described in which the first clock signal(CLK1) is at H level and the second clock signal (CLK2) is at L level.

An inverted signal of the start pulse (SP) appears at the node A. Thesignal at the node B is equal to that at the node A because the firstclock signal (CLK1) is at H level. The signal at the node B is invertedby the inverter circuit in the subsequent stage, whereby an invertedsignal of the signal at the node B appears at the node C. The signal atthe node C does not appear at the node D because the second clock signal(CLK2) is at L level and the switch is closed.

Next, operation will be described in which the first clock signal (CLK1)is at L level and the second clock signal (CLK2) is at H level.

The signal at the node C transfers to the node D, and the signal at thenode C is reflected in and appears at the node D. Then, the signal atthe node D is inverted by the inverter circuit, whereby the invertedsignal of the signal at the node D appears at the node E. After that,the first clock signal (CLK1) and the second clock signal (CLK2) arealternately at H level, so that the circuit illustrated in FIGS. 20A and20B can function as a shift register.

A shift register including the pulse output circuits shown in thisembodiment can be used for a source line driver circuit and a gate linedriver circuit. Note that a signal may be output from the shift registervia a logic circuit or the like so that a desired signal can beobtained.

The dynamic circuit described in this embodiment includes an ERMOScircuit. The ERMOS circuit includes the resistor and the thin filmtransistor shown in Embodiments 1 to 3. Accordingly, the dynamic circuithas good dynamic characteristics.

Embodiment 5

In this embodiment, an example of a display device including aprotective circuit will be described with reference to FIG. 21 and FIGS.22A and 22B.

FIG. 21 illustrates an overall view of a display device. A source linedriver circuit 501, a first gate line driver circuit 502A, a second gateline driver circuit 502B, and a pixel portion 503 are formed over asubstrate 500. In the pixel portion 503, a part surrounded by a dottedframe 510 is one pixel. FIG. 21 illustrates an example where the firstgate line driver circuit 502A and the second gate line driver circuit502B are used as a gate line driver circuit; however, only one of themmay be used as a gate line driver circuit. In the pixel of the displaydevice, a display element is controlled by a thin film transistor.Signals (clock signals, start pulses, and the like) for driving thesource line driver circuit 501, the first gate line driver circuit 502A,and the second gate line driver circuit 502B are input from the outsidevia flexible printed circuits (FPCs) 504A and 504B.

Furthermore, a protective circuit 550 is provided between the first gateline driver circuit 502A and the pixel portion, and a protective circuit551 is provided between the source line driver circuit 501 and the pixelportion. The protective circuits 550 and 551 are connected to wiringsextending from the first gate line driver circuit 502A and the sourceline driver circuit 501 to the pixel portion 503. By providing theprotective circuits 550 and 551, even when noise is input together withsignals or power supply voltages, it is possible to prevent malfunctionof the circuit in the subsequent stage or degradation or destruction ofa semiconductor element due to the noise. Thus, reliability and yieldcan be increased.

Next, a circuit structure of the protective circuits 550 and 551illustrated in FIG. 21 will be specifically described with reference toFIGS. 22A and 22B.

A protective circuit illustrated in FIG. 22A includes diode-connectedn-channel thin film transistors 560 to 567 functioning as a protectivediode, and a resistor 568. Note that in the diode-connected n-channelthin film transistors, the side of a gate terminal and a first terminalis an anode and the side of a second terminal is a cathode.

The anode of the diode-connected n-channel thin film transistor 560 isconnected to a wiring to which a low power supply potential VSS issupplied. The anode of the diode-connected n-channel thin filmtransistor 561 is connected to the cathode of the diode-connectedn-channel thin film transistor 560, and the cathode of thediode-connected n-channel thin film transistor 561 is connected to awiring 569. The anode of the diode-connected n-channel thin filmtransistor 562 is connected to the wiring 569. The anode of thediode-connected n-channel thin film transistor 563 is connected to thecathode of the diode-connected n-channel thin film transistor 562, andthe cathode of the diode-connected n-channel thin film transistor 563 isconnected to a high power supply potential VDD. The diode-connectedn-channel thin film transistors 564 to 567 are connected in a mannersimilar to that of the diode-connected n-channel thin film transistors560 to 563. The resistor 568 is connected in series to a terminal towhich an input potential Vin is input and a terminal from which anoutput potential Vout is output.

Operation of the protective circuit illustrated in FIG. 22A will bedescribed below.

When the input potential Vin from the driver circuit is extremely high,specifically, when the input potential Vin is higher than the sum of thehigh power supply potential VDD and the forward voltage drop of thediode-connected n-channel thin film transistors 562 and 563, thediode-connected n-channel thin film transistors 562 and 563 are turnedon and the wiring 569 has a potential corresponding to the sum of thehigh power supply potential VDD and the forward voltage drop of thediode-connected n-channel thin film transistors 562 and 563.

On the other hand, when the input potential Vin from the driver circuitis extremely low, specifically, when the input potential Vin is lowerthan the difference between the low power supply potential VSS and theforward voltage drop of the diode-connected n-channel thin filmtransistors 560 and 561, the diode-connected n-channel thin filmtransistors 560 and 561 are turned on and the wiring 569 has a potentialcorresponding to the difference between the low power supply potentialVSS and the forward voltage drop of the diode-connected n-channel thinfilm transistors 560 and 561.

Thus, the output potential Vout of the protective circuit can be keptwithin a given range.

Note that this embodiment shows the structure including thediode-connected n-channel thin film transistors 564 to 567 that areconnected in a manner similar to that of the diode-connected n-channelthin film transistors 560 to 563. The diode-connected n-channel thinfilm transistors 564 to 567 can increase the number of current paths inthe case where the input potential Vin from the driver circuit isextremely high or low. Accordingly, the reliability of the displaydevice can be further increased.

In addition, the resistor 568 suppresses a rapid change in the potentialof the wiring 569, thereby preventing degradation or destruction of asemiconductor element in the pixel portion.

A protective circuit illustrated in FIG. 22B includes a resistor 570, aresistor 571, and a diode-connected n-channel thin film transistor 572.The resistor 570, the resistor 571, and the diode-connected n-channelthin film transistor 572 are connected in series to a wiring 573.

The resistor 570 and the resistor 571 can suppress a rapid change in thepotential of the wiring 573, thereby preventing degradation ordestruction of a semiconductor element in the pixel portion.Furthermore, the diode-connected n-channel thin film transistor 572 canprevent the flow of a reverse bias current through the wiring 573 due toa change in potential.

Note that when only the resistors are connected in series to the wiring,a rapid change in the potential of the wiring can be suppressed anddegradation or destruction of a semiconductor element in the pixelportion can be prevented. Further, when only the diode-connectedn-channel thin film transistor is connected in series to the wiring, areverse bias current due to a change in potential can be prevented fromflowing through the wiring.

Note that the structure of the protective circuit of this embodiment isnot limited to those illustrated in FIGS. 22A and 22B. The circuitdesign can be modified as appropriate as long as the circuit operatessimilarly.

The protective circuit described in this embodiment includes theresistor and the thin film transistor shown in Embodiments 1 to 3.Accordingly, the protective circuit has good dynamic characteristics.

Embodiment 6

In this embodiment, an example of a light-emitting display device willbe described as a semiconductor device including the resistor and thethin film transistor described in Embodiments 1 to 3. Here, alight-emitting display device including a light-emitting elementutilizing electroluminescence is described. Light-emitting elementsutilizing electroluminescence are classified according to whether alight-emitting material is an organic compound or an inorganic compound.In general, the former is referred to as an organic EL element, and thelatter is referred to as an inorganic EL element.

In an organic EL element, by application of voltage to a light-emittingelement, electrons and holes are separately injected from a pair ofelectrodes into a layer containing a light-emitting organic compound,and current flows. Then, the carriers (electrons and holes) arerecombined, so that the light-emitting organic compound is excited. Thelight-emitting organic compound returns to a ground state from theexcited state, thereby emitting light. Owing to such a mechanism, thislight-emitting element is referred to as a current-excitationlight-emitting element.

The inorganic EL elements are classified according to their elementstructures into a dispersion-type inorganic EL element and a thin-filminorganic EL element. A dispersion-type inorganic EL element has alight-emitting layer where particles of a light-emitting material aredispersed in a binder, and its light emission mechanism isdonor-acceptor recombination type light emission that utilizes a donorlevel and an acceptor level. A thin-film inorganic EL element has astructure where a light-emitting layer is sandwiched between dielectriclayers, which are further sandwiched between electrodes, and its lightemission mechanism is localized type light emission that utilizesinner-shell electron transition of metal ions. Description is made hereusing an organic EL element as a light-emitting element.

The structure and operation of a pixel that can be used will bedescribed. A pixel shown here includes an n-channel thin film transistorusing an oxide semiconductor layer for a channel formation region.

FIG. 23 is a diagram illustrating an example of a pixel structure. Apixel 6400 in FIG. 23 includes thin film transistors 6401 and 6402, anda light-emitting element 6403. A gate terminal of the thin filmtransistor 6401 is connected to a gate line 6406, and a first electrodethereof is connected to a source line 6405. A gate terminal of the thinfilm transistor 6402 is connected to a second terminal of the thin filmtransistor 6401, a first terminal of the thin film transistor 6402 isconnected to a power supply line 6407, and a second terminal of the thinfilm transistor 6402 is connected to a first electrode (a pixelelectrode) of the light-emitting element 6403. Note that the powersupply line 6407 is set to a high power supply potential VDD.

A second electrode of the light-emitting element 6403 corresponds to acommon electrode 6408. The common electrode 6408 is electricallyconnected to a common potential line provided over the same substrate.Note that the second electrode of the light-emitting element 6403 (thecommon electrode 6408) is set to a low power supply potential VSS. Forexample, GND or 0 V may be set as the low power supply potential VSS.The difference between the high power supply potential VDD applied tothe power supply line 6407 and the low power supply potential VSSapplied to the second electrode is applied to the light-emitting element6403, whereby flow currents through the light-emitting element 6403 andthe light-emitting element 6403 emits light. Thus, each potential is setso that the difference between the high power supply potential VDD andthe low power supply potential VSS is equal to or higher than a forwardthreshold voltage of the light-emitting element 6403.

Next, a structure of the light-emitting element will be described withreference to FIGS. 24A to 24C. In this embodiment, the thin filmtransistor illustrated in FIG. 12A is used as a thin film transistor ofa light-emitting display device; however, any other thin filmtransistors shown in Embodiments 1 to 3 can be used as the thin filmtransistor of the light-emitting display device shown in thisembodiment.

In order to extract light emitted from the light-emitting element, atleast one of the anode and the cathode is required to transmit light. Athin film transistor and a light-emitting element are formed over asubstrate. A light-emitting element can have a top emission structure inwhich light is extracted through the surface opposite to the substrate;a bottom emission structure in which light is extracted through thesurface on the substrate side; or a dual emission structure in whichlight is extracted through the surface opposite to the substrate and thesurface on the substrate side. The pixel structure illustrated in FIG.23 can be applied to a light-emitting element having any of theseemission structures.

A light-emitting element having a top emission structure will bedescribed with reference to FIG. 24A.

FIG. 24A is a cross-sectional view of a pixel in the case where a thinfilm transistor 7001 is of an n-type and light is emitted from alight-emitting element 7002 to an anode 7005 side. In FIG. 24A, acathode 7003 of the light-emitting element 7002 is electricallyconnected to the thin film transistor 7001, and a light-emitting layer7004 and the anode 7005 are stacked in this order over the cathode 7003.The cathode 7003 can be made of a variety of conductive materials aslong as they have a low work function and reflect light. For example,Ca, Al, CaF, MgAg, or AlLi is preferably used. The light-emitting layer7004 may be formed using a single layer or a plurality of layersstacked. When the light-emitting layer 7004 is formed using a pluralityof layers, an electron-injecting layer, an electron-transporting layer,a light-emitting layer, a hole-transporting layer, and a hole-injectinglayer are stacked in this order over the cathode 7003. Not all of theselayers need to be provided. The anode 7005 is made of alight-transmitting conductive material, and for example, the anode 7005can be made of a conductive oxide having a light-transmitting property,such as indium oxide containing tungsten oxide, indium zinc oxidecontaining tungsten oxide, indium oxide containing titanium oxide,indium tin oxide containing titanium oxide, indium tin oxide, indiumzinc oxide, or indium tin oxide to which silicon oxide is added.

A region where the light-emitting layer 7004 is sandwiched between thecathode 7003 and the anode 7005 corresponds to the light-emittingelement 7002. In the case of the pixel illustrated in FIG. 24A, light isemitted from the light-emitting element 7002 to the anode 7005 side asindicated by an arrow.

Next, a light-emitting element having a bottom emission structure willbe described with reference to FIG. 24B. FIG. 24B is a cross-sectionalview of a pixel in the case where a thin film transistor 7011 is of ann-type and light is emitted from a light-emitting element 7012 to acathode 7013 side. In FIG. 24B, the cathode 7013 of the light-emittingelement 7012 is formed over a light-transmitting conductive layer 7017that is electrically connected to the thin film transistor 7011, and alight-emitting layer 7014 and an anode 7015 are stacked in this orderover the cathode 7013. A light-blocking layer 7016 for reflecting orblocking light may be formed to cover the anode 7015 when the anode 7015has a light-transmitting property. Various materials can be used for thecathode 7013, like in the case of FIG. 24A, as long as they areconductive materials having a low work function. Note that the cathode7013 is formed to a thickness that can transmit light (preferably,approximately 5 nm to 30 nm). For example, an aluminum film with athickness of 20 nm can be used as the cathode 7013. As in the case ofFIG. 24A, the light-emitting layer 7014 may be formed using either asingle layer or a plurality of layers stacked. The anode 7015 is notrequired to transmit light, but can be made of a light-transmittingconductive material like in the case of FIG. 24A. As the light-blockinglayer 7016, a metal which reflects light can be used for example;however, it is not limited to a metal film. For example, a resin towhich black pigments are added can also be used.

A region where the light-emitting layer 7014 is sandwiched between thecathode 7013 and the anode 7015 corresponds to the light-emittingelement 7012. In the case of the pixel illustrated in FIG. 24B, light isemitted from the light-emitting element 7012 to the cathode 7013 side asindicated by an arrow.

Next, a light-emitting element having a dual emission structure will bedescribed with reference to FIG. 24C. In FIG. 24C, a cathode 7023 of alight-emitting element 7022 is formed over a light-transmittingconductive layer 7027 that is electrically connected to a thin filmtransistor 7021, and a light-emitting layer 7024 and an anode 7025 arestacked in this order over the cathode 7023. Like in the case of FIG.24A, the cathode 7023 can be made of a variety of conductive materialsas long as they have a low work function. Note that the cathode 7023 isformed to a thickness that can transmit light. For example, a film of Alhaving a thickness of 20 nm can be used as the cathode 7023. Like inFIG. 24A, the light-emitting layer 7024 may be formed using either asingle layer or a plurality of layers stacked. The anode 7025 can bemade of a light-transmitting conductive material like in the case ofFIG. 24A.

A region where the cathode 7023, the light-emitting layer 7024, and theanode 7025 overlap each other corresponds to the light-emitting element7022. In the case of the pixel illustrated in FIG. 24C, light is emittedfrom the light-emitting element 7022 to both the anode 7025 side and thecathode 7023 side as indicated by arrows.

Although an organic EL element is described here as a light-emittingelement, an inorganic EL element can also be provided as alight-emitting element.

Next, the appearance and a cross section of a light-emitting displaypanel (also referred to as a light-emitting panel), which is oneembodiment of the display device, will be described with reference toFIGS. 25A and 25B. FIG. 25A is a top view of a panel in which a thinfilm transistor and a light-emitting element are sealed between a firstsubstrate and a second substrate with a sealant. FIG. 25B is across-sectional view taken along a line E-F of FIG. 25A.

A sealant 4505 is provided to surround a pixel portion 4502, source linedriver circuits 4503 a and 4503 b, and gate line driver circuits 4504 aand 4504 b, which are provided over a first substrate 4501. In addition,a second substrate 4506 is provided over the pixel portion 4502, thesource line driver circuits 4503 a and 4503 b, and the gate line drivercircuits 4504 a and 4504 b. Accordingly, the pixel portion 4502, thesource line driver circuits 4503 a and 4503 b, and the gate line drivercircuits 4504 a and 4504 b are sealed together with a filler 4507, bythe first substrate 4501, the sealant 4505, and the second substrate4506. It is preferable that a display device be thus packaged (sealed)with a protective film (such as a bonding film or an ultraviolet curableresin film) or a cover material with high air-tightness and littledegasification so that the display device is not exposed to the outsideair.

Like the source line driver circuits 4503 a and 4503 b, and the gateline driver circuits 4504 a and 4504 b, the pixel portion 4502 formedover the first substrate 4501 includes a thin film transistormanufactured using an oxide semiconductor. In FIG. 25B, a thin filmtransistor 4510 included in the pixel portion 4502 and a thin filmtransistor 4509 included in the source line driver circuit 4503 a areillustrated as an example.

In this embodiment, the thin film transistor illustrated in FIG. 12A isused as the thin film transistors 4509 and 4510; however, any other thinfilm transistors shown in Embodiments 1 to 3 can be used as the thinfilm transistor of the light-emitting display device shown in thisembodiment.

Reference numeral 4511 denotes a light-emitting element. A firstelectrode layer 4517 that is a pixel electrode included in thelight-emitting element 4511 is electrically connected to a sourceelectrode layer or a drain electrode layer of the thin film transistor4510. Note that a structure of the light-emitting element 4511 is notlimited to the stacked structure shown in this embodiment, whichincludes the first electrode layer 4517, an electroluminescent layer4512, and a second electrode layer 4513. The structure of thelight-emitting element 4511 can be changed as appropriate depending onthe direction in which light is extracted from the light-emittingelement 4511, or the like.

A partition wall 4520 is made of an organic resin film, an inorganicinsulating film, or organic polysiloxane. It is particularly preferablethat the partition wall 4520 be made of a photosensitive material andinclude an opening over the first electrode layer 4517 so that asidewall of the opening is formed as an inclined surface with continuouscurvature.

The electroluminescent layer 4512 may be formed using a single layer ora plurality of layers stacked.

A protective film may be formed over the second electrode layer 4513 andthe partition wall 4520 in order to prevent oxygen, hydrogen, moisture,carbon dioxide, or the like from entering into the light-emittingelement 4511. As the protective film, a silicon nitride layer, a siliconnitride oxide layer, a DLC layer, or the like can be formed.

A variety of signals and potentials are supplied to the source linedriver circuits 4503 a and 4503 b, the gate line driver circuits 4504 aand 4504 b, or the pixel portion 4502 from FPCs 4518 a and 4518 b.

In this embodiment, a connection terminal electrode 4515 is formed usingthe same conductive film as the first electrode layer 4517 included inthe light-emitting element 4511, and a terminal electrode 4516 is formedusing the same conductive film as the source and drain electrode layersincluded in the thin film transistors 4509 and 4510.

The connection terminal electrode 4515 is electrically connected to aterminal of the FPC 4518 a through an anisotropic conductive film 4519.

The second substrate 4506 located in the direction in which light isextracted from the light-emitting element 4511 needs to have alight-transmitting property. In that case, a light-transmitting materialsuch as a glass plate, a plastic plate, a polyester film, or an acrylicfilm is used.

As the filler 4507, an ultraviolet curable resin or a thermosettingresin can be used, in addition to an inert gas such as nitrogen orargon. For example, PVC (polyvinyl chloride), acrylic, polyimide, anepoxy resin, a silicone resin, PVB (polyvinyl butyral), or EVA (ethylenevinyl acetate) can be used. In this embodiment, nitrogen is used for thefiller 4507.

If needed, an optical film such as a polarizing plate, a circularlypolarizing plate (including an elliptically polarizing plate), aretardation plate (a quarter-wave plate or a half-wave plate), or acolor filter may be provided as appropriate on a light-emitting surfaceof the light-emitting element. Furthermore, the polarizing plate or thecircularly polarizing plate may be provided with an anti-reflectionfilm. For example, anti-glare treatment by which reflected light can bediffused by projections and depressions on the surface so as to reducethe glare can be performed.

The source line driver circuits 4503 a and 4503 b and the gate linedriver circuits 4504 a and 4504 b may be mounted as driver circuitsformed over a substrate separately prepared. Alternatively, only thesource line driver circuits or part thereof, or only the gate linedriver circuits or part thereof may be separately formed and mounted.This embodiment is not limited to the structure illustrated in FIGS. 25Aand 25B.

The light-emitting display device described in this embodiment includesthe resistor and the thin film transistor shown in Embodiments 1 to 3.Accordingly, the light-emitting display device has good dynamiccharacteristics.

Embodiment 7

In this embodiment, an example of electronic paper will be described asa semiconductor device including the resistor and the thin filmtransistor shown in Embodiments 1 to 3.

FIG. 26 illustrates active matrix electronic paper. The electronic paperin FIG. 26 uses a twisting ball display system. The twisting balldisplay system refers to a method in which spherical particles eachcolored in black and white are used for a display element and arrangedbetween a first electrode layer and a second electrode layer which areelectrode layers, and a potential difference is generated between thefirst electrode layer and the second electrode layer to control theorientation of the spherical particles, so that display is performed.

The thin film transistor 581 provided over a first substrate 580 is abottom-gate thin film transistor. A first terminal or a second terminalof the thin film transistor 581 is in contact with a first electrodelayer 587 through an opening formed in an insulating layer 585, wherebythe thin film transistor 581 is electrically connected to the firstelectrode layer 587. Spherical particles 589 each having a black region590 a, a white region 590 b, and a cavity 594 around the regions whichis filled with liquid are provided between the first electrode layer 587and a second electrode layer 588, and further sandwiched between thefirst substrate 580 and the second substrate 596. A space around thespherical particles 589 is filled with a filler 595 such as a resin (seeFIG. 26). In this embodiment, the first electrode layer 587 correspondsto the pixel electrode and the second electrode layer 588 corresponds tothe common electrode.

Instead of the twisting ball, an electrophoretic element can also beused. A microcapsule having a diameter of about 10 μm to 200 μm, inwhich transparent liquid, positively charged white microparticles, andnegatively charged black microparticles are encapsulated, is used. Inthe microcapsule that is provided between the first electrode layer andthe second electrode layer, when an electric field is applied betweenthe first electrode layer and the second electrode layer, the whitemicroparticles and the black microparticles move to opposite sides fromeach other, so that white or black can be displayed. A display elementusing this principle is an electrophoretic display element and isgenerally called electronic paper. The electrophoretic display elementhas higher reflectance than a liquid crystal display element, and thus,an auxiliary light is unnecessary, power consumption is low, and adisplay portion can be recognized in a dim place. In addition, even whenpower is not supplied to the display portion, an image which has beendisplayed once can be maintained. Accordingly, a displayed image can bestored even if a semiconductor device having a display function (whichmay be referred to simply as a display device or a semiconductor deviceprovided with a display device) is distanced from an electric wavesource.

The electronic paper described in this embodiment includes the resistorand the thin film transistor shown in Embodiments 1 to 3. Accordingly,the electronic paper has good dynamic characteristics.

Embodiment 8

In this embodiment, examples of an electronic appliance will bedescribed as a semiconductor device including the resistor and the thinfilm transistor shown in Embodiments 1 to 3.

FIG. 27A illustrates a portable game machine that includes a housing9630, a display portion 9631, a speaker 9632, operation keys 9633, aconnection terminal 9634, a recording medium reading portion 9635, andthe like. The portable game machine illustrated in FIG. 27A can havevarious functions such as a function of reading a program or data storedin a recording medium to display on the display portion, and a functionof sharing information with another portable game machine by wirelesscommunication. Note that the functions of the portable game machineillustrated in FIG. 27A are not limited to those, and the portable gamemachine can have other various functions.

FIG. 27B illustrates a digital camera that includes a housing 9640, adisplay portion 9641, a speaker 9642, operation keys 9643, a connectionterminal 9644, a shutter button 9645, an image receiving portion 9646,and the like. The digital camera having a television reception functionillustrated in FIG. 27B can have various functions such as a function ofphotographing still images and moving images; a function ofautomatically or manually adjusting the photographed images; a functionof obtaining various kinds of information from an antenna; a function ofstoring the photographed images or the information obtained from theantenna; and a function of displaying the photographed images or theinformation obtained from the antenna on the display portion. Note thatthe functions of the digital camera having a television receptionfunction illustrated in FIG. 27B are not limited to those, and thedigital camera having a television reception function can have othervarious functions.

FIG. 27C illustrates a television receiver that includes a housing 9650,a display portion 9651, speakers 9652, operation keys 9653, a connectionterminal 9654, and the like. The television receiver illustrated in FIG.27C can have various functions such as a function of converting radiowaves for television into an image signal; a function of converting animage signal into a signal which is suitable for display; and a functionof converting the frame frequency of an image signal. Note that thefunctions of the television receiver illustrated in FIG. 27C are notlimited to those, and the television receiver can have other variousfunctions.

FIG. 28B illustrates a computer that includes a housing 9660, a displayportion 9661, a speaker 9662, operation keys 9663, a connection terminal9664, a pointing device 9665, an external connection port 9666, and thelike. The computer illustrated in FIG. 28A can have various functionssuch as a function of displaying various kinds of information (e.g.,still images, moving images, and text images) on the display portion; afunction of controlling processing by various kinds of software(programs); a communication function such as wireless communication orwire communication; a function of connecting with various computernetworks by using the communication function; and a function oftransmitting or receiving various kinds of data by using thecommunication function. Note that the functions of the computerillustrated in FIG. 28A are not limited to those, and the computer canhave other various functions.

FIG. 28B illustrates a cellular phone that includes a housing 9670, adisplay portion 9671, a speaker 9672, operation keys 9673, a microphone9674, and the like. The cellular phone illustrated in FIG. 28B can havevarious functions such as a function of displaying various kinds ofinformation (e.g., still images, moving images, and text images); afunction of displaying a calendar, a date, the time, and the like on thedisplay portion; a function of operating or editing the informationdisplayed on the display portion; and a function of controllingprocessing by various kinds of software (programs). Note that thefunctions of the cellular phone illustrated in FIG. 28B are not limitedto those, and the cellular phone can have other various functions.

The electronic appliances described in this embodiment each include theresistor and the thin film transistor shown in Embodiments 1 to 3.Accordingly, the electronic appliances have good dynamiccharacteristics.

This application is based on Japanese Patent Application serial No.2008-327998 filed with Japan Patent Office on Dec. 24, 2008, the entirecontents of which are hereby incorporated by reference.

1. (canceled)
 2. A semiconductor device comprising: a transistor comprising an oxide semiconductor layer comprising a channel formation region; and a passive element comprising an electrode which comprises an oxide layer and is electrically connected to the transistor, wherein a hydrogen concentration of the oxide layer is higher than a hydrogen concentration of the oxide semiconductor layer.
 3. The semiconductor device according to claim 2, wherein the passive element is a resistor element.
 4. The semiconductor device according to claim 2, further comprising a nitride insulating layer containing hydrogen over the oxide layer.
 5. The semiconductor device according to claim 2, wherein the oxide semiconductor layer is spaced from the oxide layer.
 6. The semiconductor device according to claim 2, further comprising a light-emitting element.
 7. The semiconductor device according to claim 2, further comprising a liquid crystal element.
 8. The semiconductor device according to claim 2, wherein the transistor further comprises a gate electrode adjacent to the oxide semiconductor layer.
 9. The semiconductor device according to claim 4, wherein the nitride insulating layer is a silicon nitride layer.
 10. A semiconductor device comprising: a transistor comprising an oxide semiconductor layer comprising a channel formation region; and a passive element comprising an electrode which comprises an oxide layer and is electrically connected to the transistor, wherein the oxide semiconductor layer and the oxide layer are on a same surface, and wherein a hydrogen concentration of the oxide layer is higher than a hydrogen concentration of the oxide semiconductor layer.
 11. The semiconductor device according to claim 10, wherein the passive element is a resistor element.
 12. The semiconductor device according to claim 10, further comprising a nitride insulating layer containing hydrogen over the oxide layer.
 13. The semiconductor device according to claim 10, wherein the oxide semiconductor layer is spaced from the oxide layer.
 14. The semiconductor device according to claim 10, further comprising a light-emitting element.
 15. The semiconductor device according to claim 10, further comprising a liquid crystal element.
 16. The semiconductor device according to claim 10, wherein the transistor further comprises a gate electrode adjacent to the oxide semiconductor layer.
 17. A semiconductor device comprising: a transistor comprising an oxide semiconductor layer comprising a channel formation region; a passive element comprising an electrode which comprises an oxide layer; and a conductive layer, wherein the oxide semiconductor layer and the oxide layer are on a same surface, wherein the oxide semiconductor layer is electrically connected to the electrode through the conductive layer, and wherein the conductive layer is over the oxide layer, and wherein resistance of the oxide layer is lower than resistance of the oxide semiconductor layer.
 18. The semiconductor device according to claim 17, wherein the passive element is a resistor element.
 19. The semiconductor device according to claim 17, further comprising a nitride insulating layer containing hydrogen over the oxide layer.
 20. The semiconductor device according to claim 17, wherein the oxide semiconductor layer is spaced from the oxide layer.
 21. The semiconductor device according to claim 17, further comprising a light-emitting element.
 22. The semiconductor device according to claim 17, further comprising a liquid crystal element.
 23. The semiconductor device according to claim 17, wherein the transistor further comprises a gate electrode adjacent to the oxide semiconductor layer.
 24. A semiconductor device comprising: a transistor comprising an oxide semiconductor layer comprising a channel formation region; and a passive element comprising an electrode which comprises an oxide layer and is electrically connected to the transistor, wherein the oxide semiconductor layer and the oxide layer comprise indium and zinc, wherein the oxide semiconductor layer and the oxide layer are on a same surface, and wherein a hydrogen concentration of the oxide layer is higher than a hydrogen concentration of the oxide semiconductor layer.
 25. The semiconductor device according to claim 24, wherein the passive element is a resistor element.
 26. The semiconductor device according to claim 24, further comprising a nitride insulating layer containing hydrogen over the oxide layer.
 27. The semiconductor device according to claim 24, wherein the oxide semiconductor layer is spaced from the oxide layer.
 28. The semiconductor device according to claim 24, further comprising a light-emitting element.
 29. The semiconductor device according to claim 24, further comprising a liquid crystal element.
 30. The semiconductor device according to claim 24, wherein the transistor further comprises a gate electrode adjacent to the oxide semiconductor layer. 